WO2011129023A1

WO2011129023A1 - Heteromorphic porous hollow fiber membrane, method for producing heteromorphic porous hollow fiber membrane, module using heteromorphic porous hollow fiber membrane, filtration device, and water treatment method

Info

Publication number: WO2011129023A1
Application number: PCT/JP2010/063772
Authority: WO
Inventors: 宏和藤村; 橋野　昌年; 久保田　昇; 秀人松山
Original assignee: 旭化成ケミカルズ株式会社
Priority date: 2010-04-16
Filing date: 2010-08-13
Publication date: 2011-10-20
Also published as: JP5893093B2; EP2559478A4; US20150174809A1; TW201137197A; CA2760391A1; JP2014240071A; US9821501B2; JPWO2011129023A1; US9511529B2; PH12011502195A1; US20120125850A1; CN102574068A; EP2559478A1; CN102574068B; AU2010344678A1; SG183782A1; JP5631871B2; TWI432618B; SG10201502839SA; KR20130009941A

Abstract

Provided is a low-cost porous hollow fiber membrane which has high water permeability, abrasion resistance, and drying resistance, and which is ideal for treatment of a liquid containing inorganic and/or organic substances. The porous hollow fiber membrane is obtained from a thermoplastic resin, wherein the porous hollow fiber membrane has continuous irregularities in the outer peripheral section in the longitudinal direction of the membrane, and the outer peripheral section in the circumferential direction of the porous hollow fiber membrane is formed from a continuous irregular section.

Description

Amorphous porous hollow fiber membrane, method for producing a shaped porous hollow fiber membrane, module using the shaped porous hollow fiber membrane, filtration device, and water treatment method

The present invention relates to an irregular porous hollow fiber membrane, a method for producing an irregular porous hollow fiber membrane, a module using the irregular porous hollow fiber membrane, a filtration device, and a water treatment method. Specifically, the present invention relates to a deformed porous hollow fiber membrane having irregularities on the outer periphery, a method for producing the same, a module using the deformed porous hollow fiber membrane, a filtration device, and the deformed porous hollow fiber membrane. The present invention relates to a method for treating water containing an inorganic substance and / or an organic substance.

In recent years, porous membranes such as ultrafiltration membranes and microfiltration membranes have been used for electrodeposition paint collection, removal of fine particles from ultrapure water, production of pyrogen-free water, enzyme concentration, sterilization / clarification of fermentation broth, etc. Used in a wide range of fields such as water, sewage and wastewater treatment. In particular, porous hollow fiber membranes are widely used because they have a high membrane packing density per unit volume and can make the processing apparatus compact.

When filtering various liquids to be treated using a porous hollow fiber membrane, a part of the inorganic substance and / or organic substance contained in the liquid to be treated is adsorbed, blocked or deposited in the membrane pores or on the membrane surface. The big problem is that the water permeability is lowered by so-called fouling.

As a method for suppressing such a fouling phenomenon, Patent Document 1 discloses a physical method in which air is introduced into a hollow fiber membrane storage container to vibrate the liquid in the container and fine particles adhering to the surface of the hollow fiber membrane are removed. A clean method (so-called air scrubbing) is disclosed. Not only the casing type module disclosed in Patent Document 1, but also a non-casing type (immersion type) module that is often used in, for example, MBR (membrane separation activated sludge method), air is introduced from the lower part of the module. A method for suppressing the ring is generally used. However, this method can effectively suppress fouling of the membrane, but the phenomenon that the pores on the outer surface of the membrane are clogged by contact between the membranes, so-called “scrubbing” easily proceeds. In operation, there was a problem that the water permeability of the membrane deteriorated.

In order to further enhance the effect of this air scrubbing, a film whose shape has been devised is also disclosed. Patent Document 2 discloses a membrane that imparts a meandering crimp to a hollow fiber to suppress a decrease in membrane area due to contact between the hollow fibers and a decrease in processing performance due to liquid retention.

Patent Document 3 discloses a membrane that imparts minute protrusions to a part of the outer periphery of the hollow fiber membrane to enhance the effect of air scrubbing. Patent Document 4 also discloses a membrane having the same shape as Patent Document 3 used for dialysis.

Japanese Unexamined Patent Publication No. 60-19002 JP-A-57-194007 International Publication No. 2008/62788 JP 58-169510 A

However, it is difficult to say that the films disclosed in Patent Documents 2 to 4 are sufficiently effective in improving the air scrubbing effect and suppressing scratching.

In the shape disclosed in Patent Document 2, since the crimp cycle in the longitudinal direction of the snake hollow fiber is as long as several mm to several tens mm, the flow of the liquid cannot be controlled over the entire membrane surface. As a result, fouling occurs and the effect cannot be obtained sufficiently. Furthermore, since the angle at which the membranes come in contact with each other or the membrane may be bent and contacted by air scrubbing, the effect of suppressing scratching is small, and the deterioration of water permeability cannot be sufficiently suppressed.

Since the membrane disclosed in Patent Document 3 also has protrusions only on a part of the circumference constituting the outer peripheral portion of the hollow fiber membrane, the effect of improving the actual liquid performance is small, and the abrasion is sufficient. Cannot be suppressed.

Furthermore, in addition to the above-mentioned problems, in the case of a non-casing type (immersion type) module, drying of the membrane also becomes a problem. Hydrophobic membranes need to be hydrophilized with a liquid having a low surface tension (such as ethanol) because water does not pass through the pores unless high pressure is applied in a dry state. Membranes as products are often stored and shipped in a state where the membrane is impregnated with a moisturizing liquid such as glycerin or surfactant so that it can be immediately filtered at low filtration pressure without being hydrophilized during use. . However, the membrane may dry out if it takes a long time to remove the membrane module from the bag and attach it to the facility and start filtration (especially for large facilities). Since the dried membrane portion cannot be used for filtration, the entire membrane may not be effectively used in actual use. Regarding the problem of the drying of the film, the film described in Patent Document 2 has a large crimp shape, so that the effect of retaining the moisturizing liquid cannot be obtained. Since there is a protrusion only on the part, there is almost no effect.
Therefore, a porous hollow fiber membrane having high real liquid water permeability, high scratch resistance, and dry resistance has not been obtained so far.

The problem to be solved by the present invention is a low-cost, high water permeability performance suitable for the treatment of a liquid containing an inorganic substance and / or an organic substance, and a variant having improved scratch resistance and dry resistance. It is intended to provide a porous hollow fiber membrane, a method for producing an irregular porous hollow fiber membrane, a module using the irregular porous hollow fiber membrane, a filtration device, and a water treatment method.

As a result of intensive studies to solve the above problems, the present inventors have irregularities that are continuous in the longitudinal direction of the outer peripheral portion of a porous hollow fiber membrane made of a thermoplastic resin, and the hollow fiber membrane. The present inventors have found that it is extremely important to make the outer peripheral part of a continuous concave-convex part into a shape that is water permeability, scratch resistance, and dry resistance in an actual liquid.

That is, the present invention is as follows.
(1) A porous hollow fiber membrane made of a thermoplastic resin, having irregularities that are continuous in the longitudinal direction of the outer periphery, and the outer periphery of the hollow fiber membrane is composed of continuous irregularities. Porous hollow fiber membranes,
(2) A sum of the length from the center of the porous hollow fiber membrane to the top of the convex portion and the length from the center of the porous hollow fiber membrane to the bottom of the concave portion is the adjacent porous hollow fiber The deformed porous hollow fiber membrane according to (1), which is smaller than the center-to-center distance of the membrane,
(3) The unevenness is formed by a plurality of concave portions and a plurality of convex portions provided on the outer peripheral portion, and the opening ratio of the concave portions is higher than the opening ratio of the convex portions (1) Or the deformed porous hollow fiber membrane according to (2),
(4) The irregularly shaped porous hollow fiber membrane according to any one of (1) to (3), wherein a difference in height between the bottom portion and the top portion of the unevenness is 1 μm to 320 μm.
(5) The outer surface of the deformed porous hollow fiber membrane has a value obtained by dividing the outer surface area ratio of the recesses by the outer surface area ratio of the protrusions from 1.01 to 2.00 or less. The deformed porous hollow fiber membrane according to any one of (1) to (4),
(6) The unevenness is formed by a plurality of concave portions and a plurality of convex portions provided on the outer peripheral portion, and a ratio of surface hole diameters of the concave portions and the convex portions is 0.5 to 1.5. The deformed porous hollow fiber membrane according to any one of (1) to (5),
(7) The concave and convex portions are formed by at least a plurality of concave portions provided in the outer peripheral portion, and the proportion of the concave portions in the entire outer peripheral portion in the film cross section along the direction orthogonal to the film longitudinal direction is 5% or more and 100. % Of the deformed porous hollow fiber membrane according to any one of (1) to (6),
(8) The irregularly shaped porous according to any one of (1) to (7), wherein the proportion of the irregularities in the outer circumferential length in the membrane cross section of the irregularly shaped porous hollow fiber membrane is 30% or more Hollow fiber membrane,
(9) The irregularly shaped porous hollow fiber membrane according to any one of (1) to (8), wherein the irregularly shaped porous hollow fiber membrane is a porous membrane having an isotropic three-dimensional network structure,
(10) The deformed porous hollow fiber according to any one of (1) to (9), wherein an aspect ratio of an outer surface hole of the deformed porous hollow fiber membrane is 0.3 to 3.0 film,
(11) The irregularly shaped porous hollow fiber membrane according to any one of (1) to (10), wherein the unevenness has a width of 1 μm to 500 μm,
(12) The deformed porous hollow fiber membrane according to any one of (1) to (11), wherein the number of the irregularities in the outer peripheral portion is 1 or more and 300 or less,
(13) The irregularly shaped porous hollow fiber membrane according to any one of (1) to (12), wherein the thermoplastic resin contains polyvinylidene fluoride and polyolefin.
(14) Discharge direction by discharging a melt-kneaded product containing a thermoplastic resin and an organic liquid from a discharge port of a modified nozzle for hollow fiber molding, and cooling and solidifying the melt-kneaded product discharged from the modified nozzle After forming into a hollow fiber having a deformed cross section in a cross section perpendicular to the shape, a deformed porous hollow fiber membrane is obtained by extracting and removing the organic liquid from the hollow fiber-shaped material. In the method for producing a porous hollow fiber membrane, an inorganic fine powder is kneaded in the melt-kneaded product, and a method for producing a deformed porous hollow fiber membrane,
(15) The deformed nozzle is characterized in that the shape on the side forming the outer peripheral portion of the hollow fiber-like object is formed by a plurality of concave portions and convex portions arranged alternately along the circumferential direction (14). ) A method for producing the deformed porous hollow fiber membrane according to
(16) The deformed porous hollow fiber membrane according to (14) or (15), wherein the hollow fiber-like material and the porous hollow fiber membrane have protrusions continuous in the longitudinal direction of the membrane. Manufacturing method,
(17) The method for producing a deformed porous hollow fiber membrane according to any one of (14) to (16), wherein a pressure at the time of discharging the melt-kneaded product from a nozzle is from 100 kPa to 900 kPa,
(18) The melt-kneaded material is idled in the idle running portion until it is cooled and solidified after being discharged from the irregular nozzle, and the melt-kneaded product from a direction not parallel to the idle running direction of the melt-kneaded product in the idle running portion. (14) to (17), the method for producing a deformed porous hollow fiber membrane according to any one of (14) to (17), wherein wind is applied to an object at an angle.
(19) The method for producing a deformed porous hollow fiber membrane according to any one of (14) to (18), wherein the thermoplastic resin is composed of polyvinylidene fluoride, polyolefin, and a blend thereof.
(20) The method for producing a deformed porous hollow fiber membrane according to any one of (14) to (19), wherein the plasticizer is hydrophobic.
(21) The resin temperature when the melt-kneaded material is supplied from the extruder to the deformed nozzle and the resin temperature when discharged from the discharge port are measured by a plastmill. The method for producing a deformed porous hollow fiber membrane according to any one of (14) to (20), wherein the temperature is higher than a torque inflection temperature,
(22) A hollow fiber membrane module having the deformed porous hollow fiber membrane according to any one of (1) to (13),
(23) A membrane filtration device comprising the hollow fiber membrane module according to (22).
(24) A water treatment method for filtering a liquid to be treated containing at least one of an inorganic substance and an organic substance using the membrane filtration device according to (23),
It is.

ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the irregular-shaped porous hollow fiber membrane which is suitable for the process of the liquid containing an inorganic substance and / or an organic substance at low cost, and has high surface-opening property, ie, high water permeability, irregular-shaped porosity A hollow fiber membrane, a module using the irregular porous hollow fiber membrane, a filtration device, and a water treatment method can be obtained.

It is the schematic explaining an example of embodiment of the irregular shaped porous hollow fiber membrane which concerns on embodiment of this invention. It is sectional drawing which shows a cross section perpendicular | vertical to the longitudinal direction of the deformed porous hollow fiber membrane of FIG. FIG. 3 is an enlarged view of a part of the cross-sectional view of FIG. 2, illustrating the height and width of the unevenness. It is a schematic diagram of the three-dimensional network structure of the irregular shaped porous hollow fiber membrane which concerns on this embodiment. It is a schematic diagram of the three-dimensional network structure of the irregular shaped porous hollow fiber membrane which concerns on this embodiment. It is a schematic diagram of the spherical structure of the irregular shaped porous hollow fiber membrane which concerns on this embodiment. It is a schematic block diagram explaining the hollow fiber membrane shaping | molding apparatus which concerns on the manufacturing method of the deformed porous hollow fiber membrane of this embodiment. It is a schematic diagram which shows the example of the deformed nozzle for hollow fiber shaping | molding for manufacturing the deformed porous hollow fiber membrane which concerns on this embodiment. It is a figure which shows the structure of a hollow fiber membrane module. It is a block diagram which shows an example of the filtration apparatus of a pressure filtration system. 2 is a torque curve obtained by measuring the melt-kneaded material discharged in Example 1 with a plast mill. 2 is an electron micrograph of the cross section of the deformed porous hollow fiber membrane obtained in Example 1 at a magnification of 60 times. 2 is an electron micrograph at a magnification of 5000 times near the apex of the outer surface convex portion of the deformed porous hollow fiber membrane obtained in Example 1. FIG. 2 is an electron micrograph at a magnification of 5000 times near the bottom of the outer surface concave portion of the deformed porous hollow fiber membrane obtained in Example 1. FIG. 4 is an electron micrograph of a cross section of the porous hollow fiber membrane obtained in Comparative Example 3 at a magnification of 60 times. 4 is an electron micrograph at a magnification of 5000 times of the outer surface of a deformed porous hollow fiber membrane obtained in Comparative Example 3. FIG. 6 is an electron micrograph of a cross section of a deformed porous hollow fiber membrane obtained in Comparative Example 5 at a magnification of 60 times. It is a table | surface shown about the production conditions of the hollow fiber membrane which concerns on an Example. It is a table | surface shown about the production conditions of the hollow fiber membrane which concerns on an Example. It is a table | surface shown about the production conditions of the hollow fiber membrane which concerns on an Example. It is a table | surface shown about the production conditions of the hollow fiber membrane which concerns on an Example and a comparative example. It is a table | surface shown about the evaluation result of the various physical properties and real liquid performance of the porous hollow fiber membrane which concerns on an Example. It is a table | surface shown about the evaluation result of the various physical properties and real liquid performance of the porous hollow fiber membrane which concerns on an Example. It is a table | surface shown about the evaluation result of the various physical properties and real liquid performance of the porous hollow fiber membrane which concerns on an Example. It is a table | surface shown about the evaluation result of various physical properties and real liquid performance of the porous hollow fiber membrane which concerns on an Example and a comparative example.

Hereinafter, a mode for carrying out the present invention (hereinafter referred to as the present embodiment) will be described in detail. In addition, this invention is not limited to the following embodiment, It can change and use variously within the range of the summary.

<Atypical porous hollow fiber membrane>
First, the deformed porous hollow fiber membrane according to the present embodiment will be described with reference to FIGS. FIG. 1 is a schematic diagram illustrating the configuration of a deformed porous hollow fiber membrane according to the present embodiment. FIG. 2 is a cross-sectional view showing a cross section perpendicular to the longitudinal direction of the irregular porous hollow fiber membrane of FIG.

The irregularly shaped porous hollow fiber membrane 1 according to the present embodiment is made of a thermoplastic resin, and as shown in FIG. 1, has a substantially cylindrical shape with an opening 2 in the center portion, and its outer peripheral portion is It is a porous hollow fiber membrane composed of irregularities 3 continuous in the longitudinal direction. The “outer peripheral part” means the outer surface part of the porous hollow fiber membrane. The “longitudinal direction” means a direction perpendicular to the outer circumference circle of the deformed porous hollow fiber membrane 1 (that is, the direction in which the opening 2 extends and indicated by the arrow X in FIG. 1). “Having unevenness in the longitudinal direction” means a cross section in an outer circumferential direction orthogonal to the longitudinal direction of the irregular porous hollow fiber membrane 1 (hereinafter referred to as a cross section of the irregular porous hollow fiber membrane 1) at an arbitrary location. Means substantially the same concavo-convex structure. Each unevenness extends along the longitudinal direction of the deformed porous hollow fiber membrane 1. Therefore, substantially the same uneven structure is formed on the cut surface regardless of the cutting position of the irregular porous hollow fiber membrane 1.

By adopting such a membrane shape, (1) the flow of the membrane surface at the time of filtration is disturbed so that high actual liquid permeability can be exhibited. (2) The location where the membranes are easily contacted is limited to the convex portion. Thus, it is possible to suppress a decrease in water permeability due to rubbing, and (3) it is easy to hold the moisturizing agent in the concave portion, thereby improving dry resistance.

Further, the concave and convex portions included in the irregularities are convex on the outer side of the outer peripheral portion of the deformed porous hollow fiber membrane 1 (the center of curvature is on the inner side of the outer peripheral portion of the deformed porous hollow fiber membrane 1). The portion that is a region) is a convex portion 3A, and the portion that is concave outside the outer peripheral portion of the membrane (the region whose center of curvature is outside the outer peripheral portion of the deformed porous hollow fiber membrane 1) is referred to as a concave portion 3B. In addition, even when it does not have any one of the concave portion and the convex portion, irregularities are formed on the outer peripheral portion. For example, when there is no convex portion, the concave portions are adjacent to each other at the top portion, and a cross-sectional mountain is formed between the concave portions. However, the pointed portion is not a region where the center of curvature is on the inside, so it does not become a convex portion. On the other hand, when there is no concave portion, the concave portions are adjacent to each other at the valley portion, and a pointed groove is formed between the convex portions, but this groove is not a region where the center of curvature is outside. It will not be a recess.

Further, in the case of a film having a small number of irregularities, a film having a circumference (line) concentric with the inner diameter as a part of the outer periphery can be obtained in the same manner as a normal circular film. In this case, the outer peripheral portion concentric with the inner diameter is defined as a circumferential portion, and is clearly distinguished from the convex portion formed by the above-described protrusion. Since there is no circumferential part and the outer peripheral part is composed of a concave part and a convex part, high actual liquid performance and scratch resistance can be realized.

(Uneven shape)
Next, the unevenness | corrugation formed in the outer peripheral part of said irregular shaped porous hollow fiber membrane 1 is demonstrated. FIG. 3 is an enlarged view of a part of the cross-sectional view of FIG. 2 (region Y surrounded by an alternate long and short dash line), and is a diagram illustrating the height and width of the unevenness.

The height and width of the irregularities and the number of irregularities in the outer peripheral part of the membrane cannot be defined unconditionally depending on the outer peripheral length of the hollow fiber membrane or the height and width of the irregularities, but being in the following range is sufficient for the effect of the present invention It is preferable in exhibiting.

The height of the irregularities is preferably 1 μm or more and 320 μm or less. The height of the concavo-convex portion referred to here is a portion where the thickness of the deformed porous hollow fiber membrane 1 (distance from the inner surface of the opening 2 to the outer peripheral portion) is the thinnest (usually the bottom of the dent) or a circle having no undulation When the peripheral part is formed, the length from the surface of the peripheral part to the apex of the convex part is said, and as shown in FIG. 3, the convex part (the convex part 3A in FIGS. It can be shown by the sum of the height Ha of the region to be formed and the height (depth) Hb of the region where the recess 3B is formed. If the height of the irregularities is 1 μm or more, high cleaning recovery and scratch resistance can be exhibited, and if it is 320 μm or less, the film can be integrated at a practical filling rate when modularized. it can. More preferably, they are 5 micrometers or more and 200 micrometers or less, More preferably, they are 10 micrometers or more and 160 micrometers or less.

The width of the unevenness is preferably 1 μm or more and 500 μm or less. The width of the concavo-convex portion referred to here is the width of the region where the convex portion and the concave portion are formed, and is represented by the sum of the convex portion width Wa and the concave portion Wb of the irregular porous hollow fiber membrane 1 as shown in FIG. It is. In actual measurement, a distance obtained by connecting the bottoms of adjacent recesses with a straight line may be measured. If the width of the irregularities is 1 μm or more, the crushing of the recesses can be sufficiently suppressed without causing collapse of the protrusions when external pressure filtration is performed. Moreover, if it is 500 micrometers or less, it will become possible to suppress effectively adhesion and deposition of an inorganic substance and / or an organic substance to the front-end | tip part of protrusion by the complicated flow of the fluid in the film surface vicinity. The width of the unevenness is more preferably 5 μm to 400 m, and still more preferably 10 μm to 300 μm.

Here, the width Wb of the concave portion is preferably equal to or smaller than the maximum width of the width Wa of the convex portion, and the height Ha of the convex portion is preferably equal to or smaller than the height Hb of the concave portion. When the convex portion and the concave portion have the relationship shown above, the top of the convex portion 3A is prevented from hitting the bottom of the concave portion 3B, and the deterioration of the water permeability of the bottom of the concave portion 3B due to scratching is prevented. A decrease in the water permeability of the porous hollow fiber membrane 1 is suppressed. Furthermore, with respect to the retention of the moisturizing agent, the above-described shape reduces the influence of the membranes being rubbed together during transportation or the like to remove the moisturizing agent on the surface of the membrane, so that higher dry resistance can be exhibited.

It is preferable that the number of strips in the outer peripheral portion of the irregular porous hollow fiber membrane 1 that is the number of concave and convex portions is 1 or more and 300 or less. If it is 1 line or more, it is possible to cause a complicated flow near the film surface and prevent adhesion and deposition of inorganic and / or organic substances on the film surface. Protrusions can be accurately formed on the outer periphery of the thread porous membrane. More preferably, it is 8 or more and 200 or less, More preferably, it is 12 or more and 150 or less.

The shape of the unevenness is not particularly limited, and examples thereof include various shapes such as a convex shape and a concave shape.

Furthermore, as shown in FIG. 4, the unevenness | corrugation formed in the outer peripheral part of the irregular shaped porous hollow fiber membrane 1 is the length from the center C of the irregular shaped porous hollow fiber membrane 1 (1A, 1B) to the vertex of the convex part 3A. It is r ₁ and the profiled porous hollow fiber membrane 1 (1A, 1B) the sum of the length r ₂ from the center C to the bottom of the recess 3B of the porous hollow fiber membrane 1A adjacent, 1B distance L between centers of It is preferable to be smaller. Thereby, even when adjacent deformed porous hollow fiber membranes 1 are rubbed by vibration or the like, the apex of the convex portion 3A is prevented from hitting the bottom of the concave portion 3B. Therefore, the abrasion resistance of the irregular porous hollow fiber membrane 1 is enhanced, and the deterioration of the water permeability of the bottom of the recess 3B due to abrasion is prevented, and as a result, the degradation of the water permeability of the irregular porous hollow fiber membrane 1 is suppressed. .

In addition, the length from the center C of the convex portion 3A of the irregular porous hollow fiber membrane 1 to the apex of the convex portion 3A, the length from the center C of the irregular porous hollow fiber membrane 1 to the bottom of the concave portion 3B, and the irregular shape The center-to-center distance L of the porous hollow fiber membrane 1 can be measured as follows. First, a microscope photograph of two hollow fiber membrane cross sections is prepared. The magnification of a photograph should just be a magnification which can see the whole cross section of a film | membrane. The cross-sectional photographs of the two films may be the same photograph, or may be photographs of different locations as long as the films have substantially the same structure in the longitudinal direction. A cardboard is pasted on the back side of these two photographs, and cut off with scissors along the outer periphery of the film to replace the actual film cross section. For the center-to-center distance, the intersection of the major axis and the minor axis of the inner diameter is adopted as the center point of each film cross section. The arrangement in which the distance between the two center points becomes the shortest is determined while rotating the two film cross sections (photo cut out), and then the distance between the centers is measured with a ruler. Thereafter, the center distance L is obtained by converting the actual distance according to the magnification of the photograph. Further, on the same photograph, the length r ₁ from the center point to the convex portion (that is, the point farthest from the center point) and the length r ₂ from the center point to the concave portion (the point on the outermost part from the center point) are measured. The length L between the center distance L and the sum of r ₁ and r ₂ is compared. The above measurement can be suitably and suitably performed when the film is small. In addition, if there is no problem that the hollow fiber membrane is small and difficult to handle, it is also possible to suitably use two actual membrane cross-sections and measure them on a microscope.

The value obtained by dividing the center distance L by the sum of r ₁ and r ₂ is preferably 1.01 to 1.50, more preferably 1.03 to 1.25, and most preferably 1.05 to 1. 15 or less. If the value obtained by dividing the center-to-center distance L by the sum of r ₁ and r ₂ is 1.50 or less, the yarn bundle filled in the membrane module does not become too thick, and as a result, an economically sufficient membrane filling rate is obtained. It can be secured.

Further, if the above relationship is satisfied in a cross section perpendicular to the longitudinal direction at any position in the longitudinal direction of the deformed porous hollow fiber membrane 1, the scratch resistance of the deformed porous hollow fiber membrane 1 is improved. The improvement in water permeability becomes remarkable.

In addition, in order to improve the strength of the irregular porous hollow fiber membrane 1, a structure having a porous support layer and / or a braided cord support on the inner surface side of the aperture 2 of the irregular porous hollow fiber membrane 1 It is good. When the irregular porous hollow fiber membrane 1 is a multilayer membrane, the thickness of the outermost layer having irregularities may be constant, or the region where the convex portions are formed is the region where the concave portions are formed. It may be larger or smaller than the thickness.

(Thermoplastic resin)
The thermoplastic resin (thermoplastic polymer) constituting the deformed porous hollow fiber membrane 1 is not easily deformable at room temperature and does not exhibit plasticity, but it exhibits plasticity by appropriate heating and can be molded. It is a resin that undergoes a reversible change back to its original elastic body when it cools down and does not cause chemical changes such as molecular structure during that time (edited by the Chemistry Dictionary Editorial Committee, Chemistry Dictionary 6 Reprint) Edition, Kyoritsu Shuppan, pages 860 and 867, 1963).

Examples of thermoplastic resins include resins described in the section of thermoplastics (pages 1069 to 1125) of 14705 Chemical Products (Chemical Industry Daily, 2005), and Chemical Handbook Application Edition, revised edition 3 (The Chemical Society of Japan) , Maruzen, 1980), pages 809-810. Specific examples include polyethylene, polypropylene, polyvinylidene fluoride, ethylene-vinyl alcohol copolymer, polyamide, polyetherimide, polystyrene, polysulfone, polyvinyl alcohol, polyphenylene ether, polyphenylene sulfide, cellulose acetate, polyacrylonitrile, and the like. . Among these, crystalline polyethylene, polypropylene, polyvinylidene fluoride, ethylene-vinyl alcohol copolymer, polyvinyl alcohol, and the like can be suitably used from the viewpoint of strength development. Furthermore, among these crystalline thermoplastic resins, hydrophobic crystalline thermoplastic resins such as polyolefins such as polyethylene and polypropylene, polyvinylidene fluoride, etc., which have high water resistance due to hydrophobicity and can be expected to be durable in the filtration of ordinary aqueous liquids. Can be more suitably used. Further, among these hydrophobic crystalline thermoplastic resins, polyvinylidene fluoride, which is excellent in chemical durability such as chemical resistance, can be used particularly suitably. Examples of the polyvinylidene fluoride include a vinylidene fluoride homopolymer and a vinylidene fluoride copolymer having a vinylidene fluoride ratio of 50 mol% or more. Examples of the vinylidene fluoride copolymer include a copolymer of vinylidene fluoride and one or more selected from ethylene tetrafluoride, propylene hexafluoride, ethylene trifluoride chloride, or ethylene. As the polyvinylidene fluoride, a vinylidene fluoride homopolymer is most preferable.

(Porous structure)
(Isotropic three-dimensional network structure)
Further, the irregular porous hollow fiber membrane 1 according to the present embodiment is formed of a porous membrane having an isotropic three-dimensional network structure. “Isotropic” means that the change in the pore diameter in the film thickness direction and the film longitudinal direction is small, and the structure is a homogeneous structure containing no macrovoids. This structure is clearly defined as a structure oriented in the longitudinal direction of the membrane typical of the stretch-opening method and a structure with a large change in pore size in the cross-sectional direction of the membrane, including macrovoids often found in the non-solvent-induced phase separation method. Different. By adopting such a homogeneous structure, both the concave and convex surfaces can be used efficiently during filtration. Further, since weak portions such as macrovoids are hardly generated, it is possible to increase mechanical strength such as pressure resistance while maintaining the water permeability of the porous hollow fiber membrane.

Isotropic means (1) no voids having a diameter of 10 μm or more in the cross section in the film circumferential direction, and (2) (pore diameter in the film longitudinal direction) / (pore diameter in the film thickness direction) in the cross section in the film longitudinal direction. ) (Hereinafter referred to as the degree of orientation) is small. If it does not contain voids and the degree of orientation is in the range of 0.25 to 4.0, it may be said to be isotropic. When having such an orientation degree, the irregular porous hollow fiber membrane 1 can exhibit high water permeability and durability as described above.

The degree of orientation is more preferably 0.3 to 3.0, still more preferably 0.5 to 2.0. The method for measuring the degree of orientation is not particularly limited, and an appropriate method may be used. For example, as described in International Publication No. 2001/53213, a deformed porous hollow fiber membrane is used. Overlay a transparent sheet on a copy of the electron microscope image of the cross section in the longitudinal direction, paint the hole part black with a black pen, etc., and then copy the transparent sheet to a blank sheet, so that the hole part is black and the non-hole part is It can be clearly distinguished from white and then obtained using commercially available image analysis software. As an electron microscope image used for measurement, an image centered on the center of the film thickness portion is used unless there is a particular problem.

Also, the three-dimensional network structure here refers to a structure in which the resin is innumerable columnar shapes and joined to each other at both ends to form a three-dimensional structure. In the three-dimensional network structure, almost all of the resin forms a columnar body, and an infinite number of resin lumps that are seen in a so-called spherical structure are hardly seen. The void portion of the three-dimensional network structure is surrounded by a columnar body of thermoplastic resin, and each portion of the void portion communicates with each other. Thus, since most of the used resin forms a columnar material that can contribute to the strength of the hollow fiber membrane, it is possible to form a high strength membrane. In addition, chemical resistance is improved. The reason why the chemical resistance is improved is not clear, but because the number of columnar materials that can contribute to the strength is large, even if some of the columnar materials are affected by the chemical, the strength of the entire film is not greatly affected. It is thought that. On the other hand, in the spherical structure, since the resin is collected in the lump, the number of columnar objects is relatively small and the strength is low. For this reason, it is considered that when a part of the columnar material is attacked by the chemical, the strength of the entire film is likely to be affected. By adopting such an isotropic three-dimensional network structure, it is possible to maintain high strength even in the convex portion, and as a result, the convex portion is not deformed during use, and the concave-convex shape can be maintained during long-term use. . A schematic diagram of an isotropic three-dimensional network structure is shown in FIG. In FIG. 5, it can be seen that the gap b is formed by joining the columnar objects a. For reference, a schematic diagram of a spherical structure is shown in FIG. In FIG. 6, it can be seen that the spherulites c are partially dense, and the gaps between the dense parts of the spherulites c are voids d.

(Surface open area ratio)
Furthermore, as a result of the study by the present inventors, in the deformed porous hollow fiber membrane 1, it is expressed that the surface porosity of the concave portion 3B in the outer peripheral portion is higher than the surface porosity of the convex portion 3A, thereby exhibiting high filtration performance. It was also found that this is preferable in terms of suppressing deterioration in water permeability due to rubbing during long-term use. The concave portion 3B referred to here is a region whose center of curvature is outside the irregular porous hollow fiber membrane 1, and is a region indicated by an arrow in FIG. Further, the convex portion 3A is a region where the center of curvature is inside the irregular porous hollow fiber membrane 1, and is a region sandwiched by the concave portions 3B in FIG. Although it is not clear that the surface opening rate of the concave portion 3B in the outer peripheral portion is higher than the surface opening rate of the convex portion 3A, the reason for suppressing the decrease in water permeability is not clear, but the open area ratio of the concave portion 3B is higher than that of the convex portion 3A. This not only improves the open area ratio of the entire membrane surface, but the membrane surface is not used for filtration at the same time. It is considered important that the surface used for filtration moves.

Further, as described above, the concave portion 3B has a high cleaning recovery property by air scrubbing or shearing, and is a surface that is not easily scratched. Therefore, it is considered that it is preferable that this recess has a higher openness, that is, a high water permeability, because the whole membrane surface can maintain higher water permeability for a long period of time. The surface porosity of the irregular porous hollow fiber membrane 1 can be determined by measuring the area ratio of the pores using image analysis software in the same manner as the measurement of the degree of orientation described above. Moreover, the electron micrograph used for the measurement of the concave portion and the convex portion is an electron micrograph of the bottom of the concave portion and the apex of the convex portion. The ratio of the surface aperture ratio of the concave portion to the surface aperture ratio of the convex portion is preferably 1.01 or more and 2.00 or less. If it is 1.01 or more, high water permeability can be exhibited, and if it is 2.00 or less, not only the concave portion but also the convex portion is used for filtration. Performance can be demonstrated. More preferably, they are 1.08 or more and 1.80 or less, More preferably, they are 1.10 or more and 1.50 or less.

Further, the opening ratio of each uneven portion may be appropriately determined depending on the purpose and is not particularly limited, but is preferably 20% or more from the viewpoint of filtration stability of the liquid to be treated containing suspended substances and the like. Preferably it is 23% or more, More preferably, it is 25% or more. From the viewpoint of increasing the mechanical strength of the surface portion, the porosity is preferably 80% or less. More preferably, it is 70% or less, More preferably, it is 60% or less.

(Ratio of recesses)
In the irregularly shaped porous hollow fiber membrane 1 of the present embodiment, it is preferable that the proportion of the recesses in the entire outer peripheral length is as large as possible within a range not impairing the scratch resistance. The concave portion here is a region indicated by an arrow in FIG. 3 as described above, and high water permeability and scratch resistance can be expressed by the large number of the concave portions having a higher hole area ratio. In addition, it is preferable from the viewpoint of dry resistance that the moisturizing agent is easily held in the recesses having a higher hole area ratio (that is, having a larger number of holes) and being easily dried. The proportion of the concave portions changes depending on the number of concaves and convexes, the height and width of the concaves and convexes. The proportion of the recesses in the entire outer peripheral length is preferably 5% or more and 90% or less, more preferably 10% or more and 80% or less, and further preferably 15% or more and 70% or less.

Here, in the case of an irregularly shaped porous hollow fiber membrane for dialysis disclosed in Patent Document 4 and the like, a dense and permeation performance formed by a non-solvent phase separation method is used to provide protrusions for the purpose of preventing the adhesion of the yarn. However, it is preferable that the number of protrusions having a poor value be as small as possible within a range not impairing the effect. As a result, a film in which a protrusion is provided on a part of a normal annular outer periphery is common. On the other hand, in the case of the deformed porous hollow fiber membrane 1 according to the present embodiment, since the entire membrane has an isotropic network structure, the decrease in water permeability performance due to the protrusion is relatively small, and the recessed portion is rather Since rubbing between the films hardly occurs, it is preferable that the ratio of the recesses in the outer peripheral length is large because high water permeability can be maintained for a long period of time. Moreover, although the reason is not certain, the cleaning recovery property by shearing of the membrane surface at the time of air scrubbing or cross flow filtration is high, and higher water permeability can be exhibited.

(Surface pore diameter)
About the hole diameter of the outer surface of the irregular porous hollow fiber membrane 1, it is preferable that the value which remove | divided the surface hole diameter of the recessed part by the surface hole diameter of a convex part is 0.5 or more and 2.0 or less. More preferably, it is 0.7 or more and 1.5 or less, and further 0.8 or more and 1.3 or less. When the ratio of the surface pore diameter of the concave portion to the surface pore diameter of the convex portion is 0.5 or more and 2.0 or less, the pore diameter distribution as the whole film is sufficiently small, and high blocking performance can be exhibited. Moreover, since the filtration resistance of a convex part and the filtration resistance of a recessed part become a near value, both a convex part and a recessed part can be utilized efficiently for filtration, and it is preferable.

About the hole shape of the outer surface of the irregularly shaped porous hollow fiber membrane 1, it is preferable that the aspect ratio of the outer surface hole is 0.3 or more and 3.0 or less. If the aspect ratio of the outer surface hole is 0.3 or more, when the stress is applied in the longitudinal direction of the hollow fiber by air scrubbing, etc., the outer surface which is the blocking layer will not crack and maintain excellent blocking performance for a long time If it is 3.0 or less, it is preferable to suppress deterioration in water permeability due to rubbing when it is shaken in the film circumferential direction by air scrubbing or the like. The aspect ratio of the outer surface hole is more preferably 0.4 or more and 2.5 or less, and further preferably 0.5 or more and 2.0 or less. The aspect ratio of the outer surface hole referred to here means (surface hole diameter in the longitudinal direction of the hollow fiber) / (surface hole diameter in the circumferential direction of the hollow fiber) on the outer surface of the deformed porous hollow fiber membrane 1. The outer surface of the deformed porous hollow fiber membrane 1 includes a convex portion, a concave portion, and a circumferential portion, and it is preferable that the aspect ratio is within the above range in all of them. As for rubbing, the irregular porous hollow fiber membrane 1 sways in the circumferential direction of the hollow fiber membrane at the time of air scrubbing, so that the effect of rubbing in this direction is large. Therefore, when the hole diameter in the circumferential direction of the hole on the outer surface is small, the influence of the hole blockage is larger, and the water permeation performance is likely to deteriorate. The aspect ratio of the outer surface hole can be obtained by arithmetically averaging the aspect ratio of each hole using image analysis software in the same manner as the measurement of the degree of orientation. If the pore diameter is about 0.1 μm to 1 μm, it is appropriate to use an electron microscope image with a magnification of about 5000 times.

As for the pore shape of the inner surface of the aperture 2 of the irregular porous hollow fiber membrane 1, it is preferable that the aspect ratio is 0.25 or more and 4.0 or less from the viewpoint of the mechanical strength. If the aspect ratio of the inner surface hole is 0.25 or more, sufficient strength in the longitudinal direction of the hollow fiber membrane, that is, tensile strength can be increased, and if it is 4.0 or less, the film thickness of the hollow fiber membrane. It is possible to increase the strength in the direction, that is, the compressive strength and burst strength, which are important mechanical strengths during external pressure filtration. The aspect ratio of the inner surface hole is more preferably 0.3 or more and 3.0 or less, and further preferably 0.5 or more and 2.0 or less. When the deformed porous hollow fiber membrane 1 is composed of one layer, the aspect ratio of the inner surface hole of the opening 2 can be obtained from a photograph of an inner surface scanning electron microscope in the same manner as the aspect ratio of the outer surface hole. it can. When the irregular porous hollow fiber membrane 1 is formed of a plurality of layers, that is, when a support or the like is provided, the cross section in the membrane longitudinal direction and the cross section in the membrane circumferential direction on the inner surface side surface of the outermost layer membrane What is necessary is just to obtain | require from the photograph of a scanning electron microscope.

(Average pore size and maximum pore size)
The average pore size and the maximum pore size of the irregularly shaped porous hollow fiber membrane 1 are preferably 0.01 to 10 μm. When the average pore size and the maximum pore size are 0.01 μm or more, the filtration resistance of the membrane is low and sufficient water permeability is obtained, and when it is 10 μm or less, a membrane having excellent separation performance is obtained. More preferably, it is 0.02 μm to 5 μm, and still more preferably 0.05 to 1 μm. If the average pore size and the maximum pore size are 0.05 μm or more, it is preferable to measure the average pore size and the maximum pore size by the method described in ASTM F: 316-86, and the average pore size is smaller than 0.05 μm and is high in measurement. When pressure is required, deformation of the membrane due to high pressure becomes a problem. Therefore, an index substance having a known particle diameter is filtered, and the index substance having an inhibition rate of 50% is set to an average pore diameter of 1%. It can be measured by setting the particle diameter of the substance to the maximum pore diameter.

It is also preferable that the value obtained by dividing the maximum pore diameter by the average pore diameter is 2.0 or less. The value obtained by dividing the maximum pore size by the average pore size is an index representing the uniformity of the pore size of the membrane. The closer this value is to 1, the more the membrane has more uniform pores. When the ratio of the surface hole diameters of the concave and convex portions described above increases, the value obtained by dividing the maximum hole diameter described later by the average hole diameter also increases. This is because the pore size distribution of the entire membrane is widened by changing the pore size distribution of the concave and convex portions. If the value obtained by dividing the maximum pore diameter by the average pore diameter is 2.0 or less, high blocking performance can be achieved. More preferably, it is 1.9 or less, More preferably, it is 1.8 or less.

(Porosity)
The porosity of the irregularly shaped porous hollow fiber membrane 1 is preferably 20% to 90%. If the porosity of the irregularly shaped porous hollow fiber membrane 1 is 20% or more, it has excellent water permeability, and if it is 90% or less, a membrane having practical strength characteristics can be obtained. is there.
In the present embodiment, the porosity of the deformed porous hollow fiber membrane 1 is the difference between the wet mass and the absolutely dry mass of the porous hollow fiber membrane impregnated with water in the pores excluding the hollow portion. Can be measured by dividing by the membrane volume excluding the hollow portion.

(Other)
The inner diameter of the irregular porous hollow fiber membrane 1 (the diameter of the opening 2) is preferably 0.1 mm to 5 mm. If the inner diameter is 0.1 mm or more, the pressure loss generated when filtered water flows through the hollow portion can be kept low, and if it is 5 mm or less, the membrane packing density per unit volume should be increased. Can be made compact. More preferably, it is 0.3 mm to 4 mm, and still more preferably 0.5 mm to 3 mm.

The film thickness of the deformed porous hollow fiber membrane 1 is preferably 0.05 mm to 2 mm. If the film thickness is 0.05 mm or more, sufficient compressive strength required for the external pressure filtration porous hollow fiber membrane can be obtained, and if it is 2 mm or less, the film packing density per unit volume is increased. Can be made compact. More preferably, it is 0.1 mm or more and 1 mm or less.

The fracture elongation of the deformed porous hollow fiber membrane 1 is preferably 50% or more. When the elongation at break is 50% or more, it has sufficient durability against physical cleaning such as air scrubbing. More preferably, it is 80% or more, More preferably, it is 100% or more.

<Method for producing irregularly shaped porous hollow fiber membrane>
Next, an example of a preferable production method for producing the deformed porous hollow fiber membrane 1 according to this embodiment will be described.

(Organic liquid)
The organic liquid used is a latent solvent for the thermoplastic resin used in the present application. In the present application, the latent solvent refers to a solvent that hardly dissolves the thermoplastic resin at room temperature (25 ° C.) but can dissolve the thermoplastic resin at a temperature higher than room temperature. It may be liquid at the melt kneading temperature with the thermoplastic resin, and does not necessarily need to be liquid at room temperature.

When the thermoplastic resin is polyethylene, examples of organic liquids include dibutyl phthalate, diheptyl phthalate, dioctyl phthalate, di (2-ethylhexyl) phthalate, diisodecyl phthalate, ditridecyl phthalate, and the like; sebacine Sebacic acid esters such as dibutyl acid; adipic acid esters such as dioctyl adipate; trimellitic acid esters such as trioctyl trimellitic acid; phosphoric acid esters such as tributyl phosphate and trioctyl phosphate; propylene glycol dicaprate; Examples thereof include glycerin esters such as propylene glycol dioleate; paraffins such as liquid paraffin; and mixtures thereof.

When the thermoplastic resin is polyvinylidene fluoride, examples of organic liquids include dimethyl phthalate, diethyl phthalate, dibutyl phthalate, dicyclohexyl phthalate, diheptyl phthalate, dioctyl phthalate, and di (2-ethylhexyl) phthalate. Phthalates; benzoates such as methyl benzoate and ethyl benzoate; phosphate esters such as triphenyl phosphate, tributyl phosphate and tricresyl phosphate; γ-butyrolactone, ethylene carbonate, propylene carbonate, cyclohexanone, And ketones such as acetophenone and isophorone; and mixtures thereof.

(Inorganic fine powder)
Examples of the inorganic fine powder include silica, alumina, titanium oxide, zirconia oxide, calcium carbonate and the like, and fine powder silica having an average primary particle diameter of 3 nm to 500 nm is particularly preferable. More preferably, it is 5 nm or more and 100 nm or less. Hydrophobic silica fine powder that is difficult to aggregate and has good dispersibility is more preferable, and hydrophobic silica having a MW (methanol wettability) value of 30% by volume or more is more preferable. The MW value here is a value of the volume% of methanol at which the powder is completely wetted. Specifically, the MW value is the volume percentage of methanol in the aqueous solution at the time when 50% by mass of silica settled when silica was added to pure water and methanol was added below the liquid level with stirring. To be determined.

As for the addition amount of the inorganic fine powder, the mass ratio of the inorganic fine powder in the melt-kneaded product is preferably 5% by mass or more and 40% by mass or less. If the proportion of the inorganic fine powder is 5% by mass or more, the effect of the inorganic fine powder kneading can be sufficiently exhibited, and if it is 40% by mass or less, stable spinning can be achieved.

The mixing ratio in the melt-kneading is such that the volume ratio obtained by dividing the mass by the specific gravity is 15% to 50% by volume of the thermoplastic resin, and the total of both the organic liquid and the inorganic fine powder is 50% to 85% by volume. The range is preferable from the viewpoint of the balance between the water permeability and strength of the obtained hollow fiber and the stability of the spinning operation which is a melt extrusion operation. The thermoplastic resin is preferably 15% by volume or more from the viewpoint of the strength and spinning stability of the resulting porous multilayer hollow fiber membrane. Moreover, it is preferable that it is 85 volume% or less from the point of the water permeability of the obtained porous multilayer hollow fiber membrane and spinning stability.

The addition of inorganic fine powder has the following three advantages.
(1) Surprisingly, the melt-kneaded material to which inorganic fine powder is added is discharged from a modified spinneret to obtain a deformed porous hollow fiber membrane. The surface openability of the surface recess is greatly improved. The reason is not clear, but it is speculated that the presence of inorganic fine powder on the outer surface of the concave portion, that is, the outer periphery of the outer peripheral portion of the deformed porous hollow fiber membrane, has an effect on the improvement of the openability. Is done.
(2) Due to the thickening effect by the inorganic fine powder, a film having an isotropic three-dimensional network structure can be easily obtained, and as a result, high mechanical strength can be exhibited.
(3) When forming a deformed porous hollow fiber membrane as in the present embodiment, since the molding stability is greatly reduced when the height and number of irregularities increase, a porous hollow fiber having sufficient irregularities on the outer peripheral portion. Although it is difficult to obtain a film, the addition of inorganic fine powder increases the viscosity of the melt-kneaded product, and remarkably improves the molding stability. As a result, it is possible to easily obtain a deformed porous hollow fiber membrane having a large proportion of recesses in the outer periphery of the membrane.

(Viscosity of melt-kneaded product)
The viscosity of the melt-kneaded product during discharge is preferably in the range of 1 Pa · sec to 1000 Pa · sec. If it is 1 Pa · sec or more, the desired uneven shape can be obtained with high precision, and if it is 100 Pa · sec or less, the melt-kneaded material can be discharged stably. As a method for improving the viscosity, it is preferable to add inorganic fine powder to the melt-kneaded product. Usually, in order to increase the viscosity, the polymer concentration is increased or a polymer having a high molecular weight is often used. However, the former tends to cause a problem that the porosity contributing to filtration is lowered, and the latter is a molding defect. By adding inorganic fine powder, it is possible to improve the viscosity of the melt-kneaded product without restrictions on the molecular weight and concentration of the polymer, and to suppress deformation of the uneven shape in the idle running part from discharging from the spinning nozzle to cooling. As a result, an irregularly shaped porous hollow fiber membrane can be obtained stably. The viscosity at the time of discharge can be obtained by measuring the shear rate (shear rate) at the time of actually discharging from the spinning nozzle using a capillograph. The viscosity of the melt-kneaded product at the time of discharge is more preferably 2 Pa · sec to 800 Pa · sec, still more preferably 5 Pa · sec to 600 Pa · sec.

(Melt kneading, extrusion method)
The mixing ratio in the melt-kneading is such that the volume ratio obtained by dividing the mass by the specific gravity is 15% to 50% by volume of the thermoplastic resin, and the total of both the organic liquid and the inorganic fine powder is 50% to 85% by volume. The range is preferable from the viewpoint of the obtained hollow fiber, the balance between water permeability and strength, and the stability of the spinning operation which is a melt extrusion operation. The thermoplastic resin is preferably 15% by volume or more from the viewpoint of the strength and spinning stability of the obtained porous hollow fiber membrane. Moreover, it is preferable that it is 50 volume% or less from the point of the water-permeable performance and spinning stability of the deformed porous hollow fiber membrane obtained.

The melt kneading of the thermoplastic resin, the organic liquid, and the inorganic fine powder can be performed using a normal melt kneading means, for example, a twin screw extruder.

Here, FIGS. 7 and 8 show schematic views of a hollow fiber membrane manufacturing apparatus including a hollow fiber forming nozzle. FIG. 7 is a schematic configuration diagram of a hollow fiber membrane manufacturing apparatus, and FIG. 8 shows an example of a discharge port of a hollow fiber forming nozzle. A hollow fiber membrane manufacturing apparatus 10 shown in FIG. 7 includes an extruder 11, a hollow fiber forming nozzle 12 (an irregular nozzle for hollow fiber forming), a suction device 13, a cooling tank 14, and a winding roller 15. . In this hollow fiber membrane manufacturing apparatus 10, the melt-kneaded product A supplied from the extruder 11 is discharged from the hollow fiber forming nozzle 12, runs idle while receiving cooling air from the suction machine 13, and then in the cooling tank 14. The melted and kneaded product is solidified through the cooling bath, and is taken up by the hollow fiber take-up roller 15 after the solidification.

In the hollow fiber molding nozzle 12, the melt-kneaded product supplied from the extruder 11 flows through the spaces provided in the extruder 1 and the hollow fiber molding nozzle 12, and the hollow fiber molding nozzle 12. It discharges from the cyclic | annular discharge outlet 17 which has a shape different from the annular | circular shape provided in the lower end. At the same time, a hollow portion forming fluid such as air or a high boiling point liquid passes through a cylindrical through-hole provided in the central portion of the hollow fiber forming nozzle 12, and is a discharge portion of a hollow portion forming fluid different from the discharge port 7 ( The ink is discharged downward from the discharge port 17A) of FIG.

The shape of the discharge port 17 of the hollow fiber molding nozzle 12 is not particularly limited as long as it is an irregular shape. Here, “an irregular shape” means that the inner peripheral portion and the outer peripheral portion of the hollow fiber membrane are not concentric, and the surface shape of the outer peripheral portion is different from the surface shape of the inner peripheral portion. That is, there is no particular limitation as long as the outer periphery of the discharge port 17 is uneven. Therefore, for example, as shown in FIG. 8 (a), it may have a shape in which a semicircular convex portion is formed on the outer peripheral portion, or a semicircular shape on the outer peripheral portion as shown in FIG. 8 (b). The shape in which the shape-shaped recessed part was formed may be sufficient, and as shown in FIG.8 (c), the convex part provided in the outer peripheral side may be rectangular shape. In the hollow fiber membrane of the present embodiment, the openability of the recesses in the outer peripheral portion of the hollow fiber is particularly improved, so that the number of recesses in the deformed porous hollow fiber membrane created using the hollow fiber molding nozzle 12 increases. Thus, the nozzle in which the concave portion or the convex portion is arranged on the outer peripheral portion without any gap is more preferable. Further, when considering the durability that the porous hollow fiber membrane does not scrape or break the uneven portion during actual filtration, as shown in FIG. 8 (a), a semicircle projecting outward at the outer peripheral portion. The discharge port 17 in which a convex portion is formed is most preferable.

Here, in discharging the melt-kneaded material from the hollow fiber molding nozzle 12, when exiting from the extruder 11, that is, when the resin temperature Te at point P1 in FIG. 7 is discharged from the discharge port 17 (spinner), That is, the temperature is preferably higher than the resin temperature Ts at the point P2 in FIG. By discharging with such a resin temperature profile, the outer surface temperature of the melt-kneaded material to be discharged is lowered, and as a result, a hollow having a high unevenness moldability and a high recess surface opening property. A yarn membrane can be obtained. Furthermore, the above Te and Ts are higher than the torque inflection temperature Tp of the melt-kneaded material measured with a plast mill, so that the formation of a stable concavo-convex shape, the improvement of the surface openability of the concave portion, the surface of the concave and convex portions This is preferable in order to reduce the difference in pore diameter. The torque inflection temperature is a phase separation temperature of the melt-kneaded material containing silica. This torque inflection temperature can be measured, for example, by the following method. That is, the melt-kneaded product (once solidified) is kneaded with a plastmill at a temperature equal to or higher than the melting point (in the case of polyvinylidene fluoride resin, about 190 ° C.) until it melts uniformly, and then the temperature is raised to make the organic liquid a thermoplastic resin. The torque increases. When a certain temperature is exceeded, the organic liquid and the thermoplastic resin become uniform, and thereafter, the viscosity decrease of the thermoplastic resin becomes dominant, and the torque decreases conversely. Here, the temperature at which the torque becomes maximum is defined as a torque inflection temperature.

By setting both the resin temperature Te when exiting the extruder 11 and the resin temperature Ts when discharging from the discharge port 17 (spinning port) to be equal to or higher than the torque inflection temperature, the occurrence of defects due to the foreign matter in which silica is agglomerated, etc. It is possible to obtain an irregularly shaped porous hollow fiber membrane having excellent quality, uniform cross-sectional pore diameter, high compressive strength, high surface openness of recesses, and narrow pore size distribution (that is, high blocking performance) with good moldability. The resin temperature Tm and the resin temperature Ts are more preferably 5 ° C. or higher, more preferably 10 ° C. or higher than the torque inflection temperature Tp, from the viewpoint of suitably exhibiting the above effects.

The pressure at the tip of the hollow fiber molding nozzle when the melt-kneaded material is discharged is preferably 100 kPa or more and 900 kPa or less. In normal spinning, the shape of the hollow fiber membrane is determined by the shape of the hollow fiber molding nozzle having irregularities at the tip of the spinning nozzle, but if the pressure at the tip is not sufficient, the irregularities of the nozzle (particularly the hollow fiber convex) The resin is not distributed sufficiently to the part). In this case, as a result, only small unevenness is imparted to the hollow fiber membrane as compared with the uneven shape of the spinneret discharge nozzle. That is, the concave portion is shallow, the convex portion is low, and the film tends to contact the apex of the convex portion and the bottom of the concave portion at the outer peripheral portion of the film. Although the actual calculation of the pressure loss at the discharge tip is complicated, within the scope of the present invention, as described in the examples, it is simple from the equivalent diameter of the annular channel, the flow velocity during discharge, and the melt viscosity of the resin. What was calculated automatically can be used suitably. When the pressure at the nozzle tip is 100 kPa or more, it is preferable to mold a suitable concavo-convex shape in which the bottom of the concave portion and the apex of the convex portion do not come into contact when the films are brought into close contact with each other. Moreover, if it is 900 kPa or less, the surface roughening (melt fracture) and the fall of elongation do not occur in spinning, and it can spin stably. The pressure at the tip is more preferably 150 kPa to 800 kPa, and further preferably 200 kPa to 600 kPa.

In addition, the winding speed (that is, the winding speed by the winding roller 15) _VL of the porous hollow fiber-like material (the material in which the melt-kneaded material is solidified and the organic liquid or the like is not extracted) is set to the melt-kneaded material in the discharge port 17. it is preferred that the dividing draft ratio at the discharge linear velocity V _S of 1.1 or more and 5.0 or less. If it is 1.1 or more, an irregularly shaped porous hollow fiber membrane can be stably produced, and if it is 5.0 or less, the concave portion has a high surface openness and the surface of the convex portion and the concave portion. A membrane having a small difference in pore size and a narrow pore size distribution can be obtained. More preferably, it is 1.5-4, More preferably, it is 1.8-3.

Further, the idle running time from when the melt-kneaded material is discharged from the hollow fiber molding nozzle 12 until it is solidified in the cooling bath 14 may be arbitrarily set to adjust the pore diameter of the membrane, etc. From about 2 seconds to about 2 seconds is preferable because a film obtained by sufficient phase separation sufficiently opens. Generally, in the thermally induced phase separation method or non-solvent phase separation method without adding silica, since the viscosity of the discharged product is low, the uneven portion disappears when the idle run time is long. An uneven hollow fiber membrane can be produced.

Further, in the idle running portion L from being discharged from the discharge port 17 until being immersed in the cooling tank 14, it is possible to improve the surface openability of the recess by applying cooling air in a direction perpendicular to the discharge direction. Preferred for. The reason is not clear, but by applying cooling air in a direction perpendicular to the discharge direction, air can accumulate in the recesses to prevent evaporation of the solvent, or because the wind does not directly hit the recesses, holes on the surface It is presumed that this is the reason for exhibiting high openability with the effect that the blockage is difficult to occur.

The hollow fiber-like melt-kneaded product extruded from the discharge port 17 (spinner) is cooled and solidified by passing through a refrigerant such as air or water, and skein or the like as required (in FIG. 7, the winding roller 15 corresponds). ). During this cooling, thermally induced phase separation of the hollow fiber is induced. In the hollow fiber-like product after cooling and solidification, the polymer-rich partial phase and the organic liquid-rich partial phase are finely separated. In addition, when the inorganic fine powder is contained and the inorganic fine powder is fine powder silica, the fine powder silica is unevenly distributed in the organic liquid concentrated partial phase. By extracting and removing the organic liquid from the cooled and solidified hollow fiber-like material, the organic liquid concentrated phase portion becomes a void. Therefore, a deformed porous hollow fiber membrane can be obtained. Further, extraction and removal of the inorganic fine powder is also preferably performed from the viewpoint of further improving the water permeability of the obtained film.

The extraction removal of the organic liquid and the extraction removal of the inorganic fine powder can be performed simultaneously if they can be extracted and removed with the same solvent. Usually extracted and removed separately.

For extraction and removal of the organic liquid, a liquid suitable for extraction that is miscible with the organic liquid without dissolving or modifying the used thermoplastic resin is used. Specifically, the contact can be performed by a technique such as immersion. The liquid is preferably volatile so that it can be easily removed from the hollow fiber membrane after extraction. Examples of the liquid include alcohols and methylene chloride. If the organic liquid is water-soluble, water can also be used as the extraction liquid.

Extraction and removal of inorganic fine powder is usually performed using an aqueous liquid. For example, when the inorganic fine powder is silica, it can be performed by first contacting with an alkaline solution to convert silica to silicate, and then contacting with water to extract and remove the silicate.

∙ Either extraction or removal of organic liquid or inorganic fine powder can be performed first. When the organic liquid is immiscible with water, it is preferable to first extract and remove the organic liquid and then extract and remove the inorganic fine powder. Usually, the organic liquid and the inorganic fine powder are mixed and coexist in the organic liquid-rich partial phase, and therefore, the inorganic fine powder can be smoothly extracted and removed, which is advantageous.

Thus, a porous hollow fiber membrane can be obtained by extracting and removing the organic liquid and the inorganic fine powder from the cooled and solidified hollow fiber extrudate.

Note that (i) before extraction and removal of organic liquid and inorganic fine powder, (ii) after extraction and removal of organic liquid, and before extraction and removal of inorganic fine powder, (iii) extraction and removal of inorganic fine powder, The hollow fiber-like material can be suitably stretched in the longitudinal direction at any stage after the extraction and removal of the organic liquid and (iv) after the extraction and removal of the organic liquid and the inorganic fine powder. Generally, when the porous hollow fiber membrane is stretched in the longitudinal direction, if the breaking elongation of the hollow fiber membrane is low, it will not be stretched to the target magnification, and it will break. Elongation is important. The porous hollow fiber membrane obtained by the production method of the present application has a high elongation at break and can be suitably stretched. Stretching improves the water permeation performance of the porous multilayer hollow fiber membrane and decreases the strength in the direction perpendicular to the longitudinal direction of the hollow fiber, that is, compressive strength and burst strength. Therefore, the draw ratio is more preferably 1.1 times or more and 3 times or less. The draw ratio here refers to a value obtained by dividing the hollow fiber length after drawing by the hollow fiber length before drawing. For example, when a hollow fiber having a hollow fiber length of 10 cm is drawn to extend the hollow fiber length to 20 cm, the draw ratio is 2 times according to the following formula.
20cm ÷ 10cm = 2
If necessary, the stretched film may be heat-treated to increase the compression resistance. The heat treatment temperature is usually preferably below the melting point of the thermoplastic resin.
In addition, a production method in which a porous support layer and / or a support such as a braid is bonded to the inner surface side of the porous hollow fiber membrane of the present invention in order to improve the strength is also a preferred embodiment. The method of bonding may be either co-extrusion of bonding in a molten state, or a method of coating after solidifying once.

<Module, filtration device and filtration method>
The deformed porous hollow fiber membrane 1 obtained as described above is used for a hollow fiber membrane module, a filtration device to which the hollow fiber membrane module is attached, a water treatment (water treatment method) using the filtration device, and the like.

Hereinafter, a hollow fiber membrane module, a filtration method and a filtration device using the hollow fiber membrane module will be described. In addition, although various aspects are assumed as a hollow fiber membrane module, in the following description, a membrane type pressure filtration system membrane module will be described as an example.

FIG. 9 is a diagram showing the configuration of the hollow fiber membrane module. As shown in FIG. 9A, the hollow fiber membrane module 20 includes a bundle (hereinafter referred to as a hollow fiber membrane bundle) 21 of the porous hollow fiber membrane 1 described above. As for the hollow fiber membrane bundle 21, the upper end part and lower end part are being fixed by fixing |

fixed part

22a, 22b. Further, the hollow fiber membrane bundle 21 and the fixing

portions

22 a and 22 b are accommodated in a pipe-like case 23. In the hollow fiber membrane module 20 having such a configuration, the liquid L to be filtered is supplied between the case 23 and the hollow fiber membrane bundle 21 from the lower part (the downward direction in the figure), and the deformed porous hollow fiber is applied by applying pressure. The to-be-filtrated liquid L is filtered with the membrane 1, and a filtrate is conveyed through the header pipe etc. which are arrange | positioned above the hollow fiber membrane module 20. FIG. As shown in FIG. 9 (b), during filtration, the liquid L to be filtered in the hollow fiber membrane module 20 moves the deformed porous hollow fiber membrane 1 from the outer surface side to the inner surface side of the porous hollow fiber membrane 1. Permeated and filtered. The fixing

portions

22a and 22b are provided with through holes 24 for supplying the liquid L and air to be filtered between the case 23 and the hollow fiber membrane bundle 21. In the hollow fiber membrane module 20, the through holes 24 are provided. Air scrubbing of the hollow fiber membrane bundle 21 is performed by supplying air.

The module in which the above-described irregularly shaped porous hollow fiber membrane 1 is integrated is assumed to have other modes. For example, the module is not limited to the above-described casing type, and may be a non-casing type. Further, the cross-sectional shape of the module is not limited to the above-described circular shape (so-called cylindrical module) but may be a square shape (so-called casket type module). Further, the raw water as the liquid to be filtered may be directly filtered through the porous hollow fiber membrane 1, or the deformed porous hollow fiber membrane is added after the addition of an oxidizing agent such as a flocculant or ozone as a pretreatment. 1 may be filtered. The filtration method (filtration method) may be a total amount filtration method, a cross flow filtration method, a pressure filtration method or a suction filtration method. Furthermore, as an operation method, air scrubbing and back pressure cleaning used for the purpose of removing the filtration target deposited on the membrane surface may be performed separately, or they may be performed simultaneously. Moreover, as a liquid used for back pressure washing | cleaning, oxidizing agents, such as sodium hypochlorite, chlorine dioxide, ozone, etc. can be used suitably.

Subsequently, a pressure filtration type filtration device will be described. FIG. 10 is a configuration diagram illustrating an example of a pressure filtration type filtration device. As shown in the figure, the filtration device 30 includes a pump 31 for supplying pressure to the hollow fiber membrane module 20, a tank 32 for storing the filtrate, a tank 33 for storing the filtrate, and back pressure washing as necessary. It is possible to suitably use an apparatus including a chemical liquid tank 34 and a liquid feed pump 35 used for the above, a pump 36 for sending air necessary for air scrubbing, a pipe 37 for draining liquid discharged during air scrubbing and backwashing, and the like.

In the filtration method (water treatment method) according to the present embodiment, low cost is realized by using the hollow fiber membrane module 20, the filtration device 30, and the filtration method provided with the above-described many irregular porous hollow fiber membranes 1. In addition, long-term stable operation is possible.

Hereinafter, the present embodiment will be described more specifically with reference to examples and comparative examples. However, the present embodiment is not limited only to these examples. In addition, the measuring method used for this Embodiment is as follows. The following measurements were all performed at 25 ° C. unless otherwise specified. Below, after explaining an evaluation method, the manufacturing method and evaluation result of an Example and a comparative example are explained.

<Evaluation method>
(1) Torque inflection temperature (° C) of melt-kneaded material
110 g of the solidified melt-kneaded product was put in a lab plast mill (manufactured by Toyo Seiki, model 30C150) and heated to 190 ° C. After the temperature increase, the mixture was kneaded at 50 rpm for about 10 minutes, and then heated to 270 ° C. at a temperature increase rate of 14 ° C./min, and the resin temperature at which the torque reached a maximum was defined as the torque inflection temperature.

(2) Extruder discharge resin temperature Te (° C.), Spinner discharge resin temperature Ts (° C.)
The extruder discharge resin temperature and the spinneret discharge resin temperature were measured by inserting a K-type thermocouple thermometer.

(3) Equivalent radius of the nozzle outlet [mm]
From the chemical engineering-commentary and exercises- (Edited by Chemical Society of Japan, 20th edition, 2005, p. 35), the equivalent circle radius was calculated by the following formula.

In addition, the cross-sectional area of the nozzle discharge port was obtained by binarizing a microscope photograph taken from the nozzle discharge direction by image analysis.

(4) Melt viscosity at discharge (Pa · sec)
For various raw material compositions used in the examples, samples obtained by cutting the unextracted film discharged during spinning to a length of about 2 mm with scissors were used for measurement. Measuring instrument by Toyo Seiki Capillograph, actually shear rate at the discharge to the resin temperature from spinneret measure the melt viscosity of 6 points between 8000Sec ^-1 from 100 sec ^-1, power-law equation for viscosity (Ravinobitchi Equation: The representative viscosity m and index n in the following formula (2) were calculated by the method of least squares. Thereafter, the melt viscosity at the time of spinning at the share rate (described in (5) below) was calculated.

(5) Share rate (1 / sec)
Rheology and die design-theory and calculation-(Japan Plastics Processing Technology Association, page 60) described in the Rabinovitch correction formula (formula (3) below) to calculate the share rate.

In addition, the index n calculated | required by said (4) was used as n. Further, the discharge amount [mm ³ / sec] of the melt-kneaded product was obtained by actual measurement.

(6) Pressure at the nozzle tip [kPa]
Using the equivalent radius of the nozzle outlet calculated in (3) and the melt viscosity calculated in (4), spinning is performed from the following formula (Hagen-Poiseuille formula) (edited by the Chemical Society of Japan, 20th edition, 2005, page 39). The pressure at the mouth tip was calculated.

(7) Draft ratio The discharge linear velocity Vs of the melt-kneaded product is expressed by the following formula based on the actually measured discharge amount [mm ³ / sec] of the melt-kneaded product and the discharge cross-sectional area [mm ² ] of the spinneret obtained by image analysis. Calculated in (5).

(5)

Next, the draft ratio was calculated by the following formula (6) from the winding speed V _L and the discharge linear speed V _S of the winder.

(8) Presence / absence of yarn diameter variation, defect, and toggro The yarn diameter variation and toggro were observed by visually observing the free running part and the water landing part during spinning. About the defect, the hollow fiber-like molded product obtained by spinning was stretched at a stretch ratio of 2.5 times for about 5000 m, and confirmed by occurrence of yarn breakage.

(9) Measurement of inner diameter (mm), convex outer diameter (mm), concave outer diameter (mm) of irregularly shaped porous hollow fiber membrane Thinly cut porous hollow fiber membrane with a razor or the like in a direction perpendicular to the longitudinal direction of the membrane The inner diameter, the outer diameter of the convex part, and the outer diameter of the concave part were measured using a microscope, and calculated from the following formulas (7) to (9) by arithmetic mean. The convex outer diameter referred to here is the diameter of a concentric circle with the inner diameter passing through the apex of the convex. The concave outer diameter is the diameter of a concentric circle passing through the apex of the concave portion (the portion where the film thickness is the thinnest).

(10) Flatness of irregularly shaped porous hollow fiber membrane The flatness was calculated from the following formula (10) from the inner major axis and inner minor axis in (1) above.

(11) Measurement of irregular height H (μm), width W (μm) and number of irregularities of irregular porous hollow fiber membrane Shape of irregularities on outer periphery of porous hollow fiber membrane cross section by scanning electron microscope A photograph taken at an arbitrary magnification that can clearly confirm the above was used. On the photo, the diameter of a circle that is concentric with the inner diameter passing through the thinnest part (usually the apex of the recess) and the diameter of the circle that is concentric with the inner diameter passing through the apex of the convex part (where the film is thickest) The difference in diameter was measured, and the height H of the unevenness was determined by the following formula. The uneven width was defined as the width of the protrusion at a position where the film thickness is half the height H of the unevenness from the thinnest portion. The number of uneven portions was obtained by taking an image of the entire film cross section and visually counting the number of uneven portions.

(12) Measurement of pure water permeability (L / m ² / hr) of irregularly shaped porous hollow fiber membrane One end of a wet hollow fiber membrane having a length of about 10 cm is sealed, and an injection needle is inserted into the hollow part at the other end. Pure water was injected into the hollow portion from the injection needle at a pressure of 0.1 MPa, the amount of pure water permeated to the outer surface was measured, and the pure water permeability was determined by the following equation. The effective membrane length refers to the net membrane length of the porous hollow fiber membrane excluding the portion where the injection needle is inserted, and π refers to the circumference.

(13) Center-to-center distance L [mm], length to convex portion r ₁ [mm], length to concave portion r ₂ [mm]
First, two microscope photographs (VHX100, manufactured by Keyence Corporation) of two hollow fiber membrane cross sections were taken at a magnification at which the entire cross section of the membrane could be seen. For the cross-sectional photographs of the two films, cardboard was pasted on the back side of these two photographs, and cut with scissors along the outer periphery of the film to replace the actual film cross-section. The intersection of the major axis and the minor axis of the inner diameter is adopted as the center point of each membrane cross section, and the arrangement in which the distance between the two center points is the shortest while rotating the two membrane cross sections (photo cut out) is determined. The distance between the center points was measured with a ruler. Thereafter, the length measured in accordance with the magnification of the photograph is converted into an actual distance, and the center distance L is obtained. Further, on the same photograph, the length r ₁ from the center point to the convex portion (that is, the point of the outer peripheral portion farthest from the central point) and the length r ₂ from the center point to the concave portion (the point of the outer peripheral portion closest to the central point) Was measured.

(14) Defects and protrusions on the outer surface of the irregular porous hollow fiber membrane (%)
It measured by the method of international publication 2001/53213. First, a copy of an electron microscope image taken from a direction perpendicular to the outer surface at a magnification that allows the shape of a large number of holes to be clearly confirmed as much as possible on the outer surface corresponding to the top of the convex portion and the bottom of the concave portion using a scanning electron microscope A transparent sheet was overlaid on the surface, and the hole portion was painted black with a black pen or the like, and then the transparent sheet was copied to a white paper, thereby clearly distinguishing the hole portion from black and the non-hole portion from white. Thereafter, the surface area ratio was determined using commercially available image analysis software.

(15) Breaking strength (MPa), elongation at break (%)
Using an Instron type tensile tester (AGS-5D manufactured by Shimadzu Corporation), the wet hollow fiber membrane is pulled at a distance between chucks of 5 cm and a pulling speed of 20 cm / min. From the load and displacement at break, the following equation (12), The breaking strength and breaking elongation were determined by (13). The membrane cross-sectional area was determined by image analysis from a micrograph of the membrane cross-section.

(16) Latex rejection (%)
Uniform latex with a particle size of 0.208 μm (manufactured by JSR Co., Ltd., trade name: STADEX, solid content 1% by mass) is diluted 100 times with 0.5% by mass SDS (sodium dodecyl sulfonate) aqueous solution, and latex A suspension having a concentration of 0.01% by mass was prepared. A sufficient amount of this latex suspension is placed in a beaker and supplied to a wet hollow fiber having an effective length of about 12 cm by a peristaltic pump at a linear velocity of 0.1 m / s from the outer surface at a pressure of 0.03 MPa. The latex suspension was filtered by discharging the permeate from both ends (open to the atmosphere). The filtrate was returned to the beaker and filtered in a closed system. Ten minutes after filtration, the permeate from both ends of the hollow fiber and the feed solution from the beaker were sampled, the absorbance at 600 nm was measured using an absorptiometer, and the latex rejection was determined by the following formula (14).

(17) Compressive strength (MPa)
One end of a wet hollow fiber having a length of about 5 cm was sealed, the other end was opened to the atmosphere, and pure water at 40 ° C. was pressurized from the outer surface by total filtration to discharge permeated water from the open end of the atmosphere. The pressurization pressure was increased from 0.1 MPa in increments of 0.01 MPa, the pressure was maintained at each pressure for 15 seconds, and the permeated water coming out from the open end of the atmosphere was sampled during the 15 seconds. While the hollow portion of the hollow fiber is not crushed, the absolute value of the permeated water amount (weight) increases as the pressurized pressure increases. However, when the pressurized pressure exceeds the compressive strength of the hollow fiber, the hollow portion is crushed and clogged. Since it starts, the absolute value of the amount of permeate decreases as the pressure increases. The pressurizing pressure at which the absolute value of the amount of permeated water was maximized was defined as the compressive strength.

(18) Maximum pore size (μm)
Measurement was performed in accordance with the maximum pore size measurement method (also known as bubble point method) described in ASTM: F316-86. The measurement was performed on a 5 cm long hollow fiber membrane using ethanol as a liquid and compressed air as a pressure gas at 25 ° C. and a pressure increase rate of 0.05 atm / second. With respect to the obtained bubble point pressure, the maximum pore diameter was calculated by the following formula (15).

When the liquid used is ethanol, the surface tension at 25 ° C. is 21.97 dynes / cm. (Edited by the Chemical Society of Japan, Basic 3rd edition of the Chemical Handbook, II-82, Maruzen, 1984)

(19) Average pore diameter (μm)
The average pore diameter was measured according to ASTM: F316-86 (also known as half-dry method). The measurement was performed on a 5 cm long hollow fiber membrane using ethanol as a liquid and nitrogen as a pressurizing gas at 25 ° C. and a pressurization rate of 0.01 atm / sec. With respect to the obtained half dry average pressure, the average pore diameter was calculated by the following formula (16).

(20) Production of pressure-type hollow fiber membrane module A pressure-type hollow fiber membrane module having a membrane area of 50 m ² was produced as follows. After bundling a plurality of porous hollow fiber membranes, the hollow portion of one end face of the hollow fiber bundle is sealed and stored in a polysulfone cylindrical module case having an inner diameter of 150 mm and a length of 2000 mm. Only 24 pieces of polypropylene rods having an outer diameter of 11 mm were placed on the other end portion in parallel with the porous hollow fiber membrane on the other end portion. A tool was attached.

The module case with the bonding jig attached on both sides was centrifugally cast with a two-component epoxy resin.

After centrifugal casting, the bonding jig and the polypropylene rod were removed, and after the epoxy bonded portion was sufficiently cured, the bonded end portion on the side subjected to the sealing treatment was cut to open the hollow portion of the hollow fiber. As described above, a pressure-type hollow fiber membrane module comprising a hollow fiber membrane bundle was obtained.

(21) Production of negative pressure type hollow fiber membrane module A negative pressure type hollow fiber membrane module having a membrane area of 25 m ² was produced in the same manner as described in International Publication No. 2004/112944.

That is, a cartridge head in which both ends of a plurality of porous hollow fiber membranes are bonded and fixed with urethane resin, and are liquid-tightly bonded and fixed to the outer periphery of one end, and a lower ring that is liquid-bonded and fixed to the outer periphery of the other end A cylindrical hollow fiber membrane module was prepared. The effective length between the filtration part interfaces of the cartridge head side and the lower ring side adhesive fixing layer was 2000 mm. The diameter of the adhesive fixing layer at both ends of the hollow fiber was about 150 mm. As described above, a negative pressure type hollow fiber membrane module was prepared.

(22) Water permeability measurement experiment 1 (pressurization) of hollow fiber membrane module
Using the hollow fiber membrane module obtained in (20), river surface water having a turbidity of 5 to 10 degrees and a water temperature of 18 to 25 ° C. was used as raw water. Permeation rate is the limit permeation rate by increasing the permeation rate step-by-step with the external pressure total filtration method by pressurization by the pump, and the transmembrane pressure difference does not increase rapidly (does not exceed 10 kPa / week in terms of 25 ° C). The amount was measured.

The filtration operation described above was a cycle operation of filtration / (backwashing and air bubbling). Each cycle is a filtration / (backwash and air bubbling) time cycle: 29 minutes / 1 minute, the backwash flow rate during backwash is 2.3 L / min / module, and the air flow rate during air bubbling is 4.6 NL / min / module.

(23) Water permeability measurement experiment 2 of hollow fiber membrane module (negative pressure)
The hollow fiber membrane module obtained in (21) was used and immersed in an activated sludge tank having a volume of 8 m ³ . Moreover, the factory waste_water | drain whose BOD is 750 mg / L was used as raw | natural water. The MLSS concentration in the activated sludge was constant at about 10 g / L. The amount of water permeation is reduced to a negative pressure in the hollow part of the membrane by a suction pump, and the amount of water permeation is increased step by step by the total filtration method, so that the transmembrane pressure difference does not increase rapidly (over 10 kPa / week in terms of 25 ° C). No) The critical water permeability was measured.

The filtration operation described above was a cycle operation of filtration / backwashing while constantly aeration of air with a membrane aeration amount of 6 Nm ³ / hour. The filtration / backwash time cycle was filtration / backwash: 9 minutes / 1 minute, and the backwash flow rate during backwashing was the same as the flow rate during filtration.

(24) Ratio of irregularities in the circumference of the outer circumference (%)
A photograph taken at an arbitrary magnification capable of clearly confirming the shape of the irregularities on the outer periphery of the cross section of the porous hollow fiber membrane was used with a scanning electron microscope. A circumferential part, a recessed part, and a convex part were distinguished on the photograph, and the ratio of the uneven part in the circumference of the outer peripheral part was calculated by the following formula.

(25) Scratch resistance (%)
Except that diatomaceous earth (manufactured by Central Silica: # 600-H) was added to the activated sludge tank to 1000 ppm in order to promote abrasion, the filtration rate of 0.5 m / day was about the same as (23). The operation was carried out for 1 month, and the pure water permeability of the hollow fiber membrane having an effective length of 10 cm before and after the operation was measured by the same method as in the above (12), and the scratch resistance was determined by the following formula.

(26) Convex height retention after rubbing (%)
The film used in (25) was sampled, and the height of the convex part after rubbing was measured in the same manner as in (11). Then, the convex part height retention after rubbing was calculated by the following formula.

(27) Drying resistance Ten hollow fiber membranes having a length of 15 cm were dried with a dryer at 45 ° C. for 24 hours, and then the pure water permeability of the dried membrane was measured in the same manner as in (12). Thereafter, the dry resistance was calculated by the following formula.

<Production and evaluation results of Examples 1 to 31 and Comparative Examples 1 to 5>
[raw materials]
The materials constituting the hollow fiber membranes of Examples 1 to 31 and Comparative Examples 1 to 5 and the hollow fiber membrane module produced from the hollow fiber membranes are selected from the following materials, respectively. The materials from which the hollow fiber membranes according to the examples and comparative examples were produced and the composition ratios thereof are shown in FIGS. 18 to 21, the respective materials are indicated by the symbols shown below. Moreover, all the composition ratios are shown using parts by mass.
Thermoplastic resin:
(R-1) Vinylidene fluoride homopolymer (manufactured by Kureha Co., Ltd., trade name: KF # 1000)
(R-2) High density polyethylene resin (Asahi Kasei Chemicals Corporation, trade name: SH800)
Organic liquid:
(R-3) Polypropylene resin (product name: PN110G, manufactured by Tokuyama Corporation)
(R-4) Cellulose acetate butyrate polymer (Mw = 65,000)
(L-1) Di (2-ethylhexyl) phthalate (manufactured by CG Esther)
(L-2) Dibutyl phthalate (manufactured by CG Esther)
Inorganic fine powder:
(L-3) Triethylene glycol (manufactured by Wako Pure Chemical Industries)
(P-1) Finely divided silica (manufactured by Nippon Aerosil Co., Ltd., trade name: AEROSIL-R972, primary particle diameter of about 16 nm)
Hydrophilic additive:
(P-2) Hydrophilic additive (polyethylene glycol, weight average molecular weight 35000, manufactured by Merck & Co., Inc.)

[Example 1]
Vinylidene fluoride homopolymer (made by Kureha Chemical Co., Ltd., trade name: KF # 1000) as a thermoplastic resin, a mixture of di (2-ethylhexyl) phthalate and dibutyl phthalate as an organic liquid, and fine silica as an inorganic fine powder (Nippon Aerosil Co., Ltd.) Manufactured and trade name: AEROSIL-R972). The composition of the melt-kneaded material to be discharged is vinylidene fluoride homopolymer: bis (2-ethylhexyl) phthalate: dibutyl phthalate: fine powder silica = 34.0: 33.8: 6.8: 25.4 (mass ratio) The melt-kneaded product is extruded at a draft ratio of 2.3 from a hollow fiber forming nozzle having 16 convex portions with a height of 200 μm and a width of 400 μm on the outer periphery of the discharge portion using air as a hollow portion forming fluid. Thus, a deformed hollow fiber shaped molding was obtained.

The resin temperature when the melt-kneaded product exited the extruder was 250 ° C., and the resin temperature when discharged from the spinning nozzle was 245 ° C. Moreover, the torque curve which measured the discharged melt-kneaded material with the plast mill is shown in FIG. The torque inflection temperature was 235 ° C.

The obtained hollow fiber-like molded product is cooled and solidified by passing it in the air at 30 ° C after running in the air for 30 cm while applying cooling air in the direction perpendicular to the discharge direction, and skeined at a speed of 30 m / min. Winded up. The resulting hollow fiber extrudate was immersed in methylene chloride to extract and remove bis (2-ethylhexyl) phthalate and dibutyl phthalate, and then dried. Next, after immersing in a 40% by mass ethanol aqueous solution for 30 minutes, it was immersed in water for 30 minutes to wet the hollow fiber membrane. Subsequently, it was immersed in 20 mass% NaOH aqueous solution at 70 degreeC for 1 hour, and also water washing was repeated, and the fine powder silica was extracted and removed. The production conditions of the hollow fiber membrane are shown in FIG. 18, and the evaluation results of various physical properties and actual liquid performance of the obtained porous hollow fiber membrane are shown in FIG.

Further, a scanning electron micrograph of the cross section of the obtained porous hollow fiber membrane at a magnification of 60 times is shown in FIG. 12, a scanning electron micrograph at a magnification of 5000 times of the outer surface convex portion vertex is shown in FIG. Scanning electron micrographs at a magnification of 5000 are shown in FIG. The surface openability of the concave portion was clearly improved as compared with the convex portion.

[Examples 2 to 9]
A porous hollow fiber membrane was produced in the same manner as in Example 1 except that the pressure at the tip of the nozzle was changed by changing the discharge speed and the winding speed from the hollow fiber molding nozzle. The production conditions of Examples 2 to 9 are shown in FIG. 18, and the evaluation results of various physical properties and actual liquid performance of the porous hollow fiber membrane are shown in FIG. When the pressure at the nozzle tip was low, the irregular shape was slightly difficult to attach as compared with Example 1, but an irregularly shaped porous hollow fiber membrane with irregularities was obtained. Moreover, the recessed part had the high surface opening rate similarly to Example 1.

[Examples 10 to 14]
Example 1 except that the direction of the cooling air in the idling portion is 0 °, 15 °, 30 °, 45 °, and 60 ° with respect to the direction parallel to the discharge direction (suction from the upper part of the discharge port), respectively. Thus, a porous hollow fiber membrane was produced. FIG. 19 shows the conditions for producing the hollow fiber membrane, and FIG. 23 shows the evaluation results of various physical properties and actual liquid performance of the obtained porous hollow fiber membrane.

[Example 15]
A porous hollow fiber membrane was produced in the same manner as in Example 1 except that the temperature setting of the extruder barrel was changed so that the resin temperature discharged from the extruder was 220 ° C. FIG. 19 shows the conditions for producing the hollow fiber membrane, and FIG. 23 shows the evaluation results of various physical properties and actual liquid performance of the obtained porous hollow fiber membrane.

[Example 16]
A porous hollow fiber membrane was produced in the same manner as in Example 1 except that the temperature setting of the spinning nozzle was changed so that the resin temperature discharged from the spinning nozzle was 210 ° C. FIG. 19 shows the conditions for producing the hollow fiber membrane, and FIG. 23 shows the evaluation results of various physical properties and actual liquid performance of the obtained porous hollow fiber membrane. Thread breakage due to defects occurred at a frequency of 2 times / 5000 m.

[Example 17]
Porous as in Example 1 except that the temperature setting of the extruder barrel and spinning nozzle was changed so that the resin temperature discharged from the extruder was 220 ° C. and the resin temperature discharged from the spinning nozzle was 210 ° C. Porous fiber membrane was produced. FIG. 19 shows the conditions for producing the hollow fiber membrane, and FIG. 23 shows the evaluation results of various physical properties and actual liquid performance of the obtained porous hollow fiber membrane. Thread breakage due to defects occurred at a frequency of 10 times / 5000 m.

[Example 18]
The composition of the melt-kneaded material to be discharged is vinylidene fluoride homopolymer: bis (2-ethylhexyl) phthalate: dibutyl phthalate: fine powder silica = 40.0: 30.8: 6.2: 23.0 (mass ratio) A porous hollow fiber membrane was produced in the same manner as in Example 1 except that. FIG. 19 shows the conditions for producing the hollow fiber membrane, and FIG. 23 shows the evaluation results of various physical properties and actual liquid performance of the obtained porous hollow fiber membrane.

[Example 19]
High-density polyethylene resin (trade name: SH800, manufactured by Asahi Kasei Chemicals Corporation) as the thermoplastic resin, dibutyl phthalate as the organic liquid, polyethylene resin: dibutyl phthalate: fine powder silica = 20.0: 56.0: 24.0 A porous hollow fiber membrane was obtained in the same manner as in Example except that (weight ratio), Te = 245 ° C., Ts = 240 ° C., and skein wound at a speed of 20 m / min. The melt-kneaded product had a Tp of 228 ° C. FIG. 20 shows the conditions for producing the hollow fiber membrane, and FIG. 24 shows the evaluation results of various physical properties and actual liquid performance of the obtained porous hollow fiber membrane.

[Example 20]
The hollow fiber-like molded product obtained in Example 1 (solidified state in which the organic liquid and silica fine powder were not removed) was held at both ends with a length of 10 cm by hand and stretched to a length of 20 cm, and then released from both ends. Thereafter, the plasticizer and fine silica were extracted and removed in the same manner as in Example 1. Further, heat treatment was performed at 140 ° C. for 30 minutes without fixing both ends of the membrane to obtain a porous hollow fiber membrane. The final yarn length was 12.5 cm (final draw ratio: 1.25 times). FIG. 20 shows the conditions for producing the hollow fiber membrane (the same conditions as in Example 1), and FIG. 24 shows the evaluation results of various physical properties and actual liquid performance of the obtained porous hollow fiber membrane.

[Example 21]
Using two extruders, the mixture of the composition of Example 1 was used as the outer layer, and the vinylidene fluoride homopolymer: bis (2-ethylhexyl) phthalate: dibutyl phthalate: finely divided silica = 36.0: 34. A two-layer porous hollow fiber membrane was prepared in the same manner as in Example 1 except that a melt-kneaded product of 8: 5.0: 24.2 (mass ratio) was simultaneously extruded from a nozzle and co-extruded to form a two-layer structure. Got. FIG. 20 shows the conditions for producing the hollow fiber membrane, and FIG. 24 shows the evaluation results of various physical properties and actual liquid performance of the obtained porous hollow fiber membrane.

[Examples 22 to 24]
As a hollow fiber molding nozzle, a porous fiber molding nozzle was used in the same manner as in Example 1 except that a hollow fiber molding nozzle having 12, 32, and 64 convex portions each having a height of 200 μm and a width of 400 μm on the outer periphery of the discharge portion was used. A hollow fiber membrane was obtained. FIG. 20 shows the conditions for producing the hollow fiber membrane, and FIG. 24 shows the evaluation results of various physical properties and actual liquid performance of the obtained porous hollow fiber membrane.

[Examples 25 to 28]
As the hollow fiber molding nozzle, the same as in Example 1 except that a hollow fiber molding nozzle having 16 convex portions (all widths are 400 μm) each having a height of 50 μm, 100 μm, 300 μm, and 400 μm on the outer periphery of the discharge portion was used. Thus, a porous hollow fiber membrane was obtained. The production conditions of the hollow fiber membrane are shown in FIG. 20 (Examples 25 to 27) and FIG. 21 (Example 28), and the evaluation results of various physical properties and actual liquid performance of the obtained porous hollow fiber membrane are shown in FIG. 25 to 27) and FIG. 25 (Example 28).

[Example 29]
A porous hollow fiber membrane was obtained in the same manner as in Example 1 except that cellulose acetate butyrate polymer (Mw = 65,000) was used as the thermoplastic resin and triethylene glycol (manufactured by Wako Pure Chemical Industries, Ltd.) was used as the organic liquid. The conditions for producing the hollow fiber membrane are shown in FIG. 21, and the evaluation results of various physical properties and actual liquid performance of the obtained porous hollow fiber membrane are shown in FIG.

[Example 30]
A porous hollow fiber membrane was obtained in the same manner as in Example 1 except that polypropylene resin (manufactured by Tokuyama Corporation, trade name: PN110G) was used as the thermoplastic resin, and dibutyl phthalate (manufactured by CG Esther Co., Ltd.) was used as the organic liquid. . The conditions for producing the hollow fiber membrane are shown in FIG. 21, and the evaluation results of various physical properties and actual liquid performance of the obtained porous hollow fiber membrane are shown in FIG.

[Example 31]
As a hollow fiber molding nozzle, a hollow fiber molding nozzle having an outer diameter of a concave portion of 2.3 mm, an inner diameter of 1.3 mm, 20 convex portions having a height of 200 μm and a width of 400 μm on the outer periphery of the discharge portion, and a speed of 45 m / min is further used. A porous hollow fiber membrane was obtained in the same manner as in Example 1 except that it was wound up in a skein. The conditions for producing the hollow fiber membrane are shown in FIG. 21, and the evaluation results of various physical properties and actual liquid performance of the obtained porous hollow fiber membrane are shown in FIG.

[Comparative Example 1]
The composition of the melt-kneaded product to be extruded is vinylidene fluoride homopolymer: bis (2-ethylhexyl) phthalate: dibutyl phthalate = 34.0: 46.0: 20.0 (mass ratio), and the air time is 0.01 A porous hollow fiber membrane was obtained in the same manner as in Example 1 except that the second (running distance was 5 mm), and Te = 240 ° C. and Ts = 230 ° C. were used. The melt-kneaded product had a Tp of 210 ° C. This melt-kneaded product containing no silica was a porous hollow fiber membrane that was difficult to spin because the irregularities were easily lost immediately after ejection from the spinneret, and that had a large flatness. Moreover, the actual liquid permeation amount of (22) and (23) was also a low value. The conditions for producing the hollow fiber membrane are shown in FIG. 21, and the evaluation results of various physical properties and actual liquid performance of the obtained porous hollow fiber membrane are shown in FIG.

[Comparative Example 2]
A porous hollow fiber membrane was produced in the same manner as in Comparative Example 1 except that the idle running time was 0.60 seconds. The obtained porous hollow fiber membrane was free of irregularities, and the outer peripheral portion was a circular porous hollow fiber membrane. The conditions for producing the hollow fiber membrane are shown in FIG. 21, and the evaluation results of various physical properties and actual liquid performance of the obtained porous hollow fiber membrane are shown in FIG.

[Comparative Example 3]
A porous hollow fiber membrane was obtained in the same manner as in Example 1 except that an annular nozzle having no irregularities on the outer peripheral portion and circular was used as a hollow fiber molding nozzle. The conditions for producing the hollow fiber membrane are shown in FIG. 21, and the evaluation results of various physical properties and actual liquid performance of the obtained porous hollow fiber membrane are shown in FIG. Moreover, the electron micrograph of the cross section of the obtained porous hollow fiber membrane of 60 times is shown in FIG. 15, and the electron micrograph of 5000 times of the outer surface is shown in FIG.

[Comparative Example 4]
Polyethylene glycol having a weight average molecular weight of 35,000 (manufactured by Merck) was used as a hydrophilic additive, and dimethylacetamide (manufactured by Kishida Chemical Co., Ltd.) was used as an organic liquid. Vinylidene fluoride homopolymer: dimethylacetamide: polyethylene glycol = 27: 57.5 : 15.5 (mass ratio) was dissolved at 70 ° C. This dissolved material was discharged as a hollow portion forming fluid with a 90% by mass aqueous solution of dimethylacetamide at a resin temperature of 70 ° C., and after passing through a free running distance of 3 mm, it was immersed in an 80 ° C. water bath to be solidified. By winding at a speed of / min, a porous hollow fiber membrane was obtained by a non-solvent induced phase separation method. In addition, when the idle running distance was larger than 3 mm, the convex portion disappeared and a normal annular shape was formed. The resulting porous hollow fiber membrane had an asymmetric structure with a dense skin layer on the outer surface and voids in the cross section. Specifically, it is difficult to spin because the unevenness tends to disappear immediately after the ejection from the spinning nozzle, and the obtained film is also a porous hollow fiber membrane having no unevenness uniformly on the outer periphery. The conditions for producing the hollow fiber membrane are shown in FIG. 21, and the evaluation results of various physical properties and actual liquid performance of the obtained porous hollow fiber membrane are shown in FIG. The outer diameter of the convex part in the table is twice the distance from the center to the point with the highest convex part, the outer diameter of the concave part is twice the distance from the center to the point with the smallest film thickness, and the unevenness height is the most convex The heights of the protrusions with high parts are described.

[Comparative Example 5]
Referring to Example 1 of Japanese Patent Application No. 2009-033866 (TIPS2-A disclosed in SCEJ 74th Annual Meeting (Yokohama, 2009) E122), the composition of the melt-kneaded product to be extruded was determined as cellulose acetate butyrate polymer: tri Example 1 except that ethylene glycol = 20.0: 80.0 (mass ratio), air time was 0.01 seconds (air travel distance was 5 mm), Te = 170 ° C., and Ts = 170 ° C. In the same manner, a porous hollow fiber membrane was obtained. Immediately after discharge from the nozzle, the unevenness tends to disappear, making it difficult to spin, and the obtained membrane was also a porous hollow fiber membrane with no unevenness on the outer periphery. A scanning electron micrograph of the cross section of the obtained porous hollow fiber membrane at a magnification of 60 times is shown in FIG. Moreover, the actual liquid permeation amount of (22) and (23) was also a low value. The conditions for producing the hollow fiber membrane are shown in FIG. 21, and the evaluation results of various physical properties and actual liquid performance of the obtained porous hollow fiber membrane are shown in FIG. The outer diameter of the convex part in the table is twice the distance from the center to the point with the highest convex part, the outer diameter of the concave part is twice the distance from the center to the point with the smallest film thickness, and the unevenness height is the most convex The heights of the protrusions with high parts are described.

According to the present invention, a modified porous hollow fiber membrane having high water permeability, scratch resistance, and drying resistance suitable for treatment of a liquid containing an inorganic substance and / or an organic substance, and production of the deformed porous hollow fiber film A method, a module using the deformed porous hollow fiber membrane, a filtration device, and a water treatment method can be obtained. The present invention has industrial applicability in the field of water treatment.

DESCRIPTION OF SYMBOLS 1 ... Atypical porous hollow fiber membrane, 2 ... Opening part, 3 ... Concavity and convexity, 3A ... Convex part, 3B ... Concave part, 10 ... Hollow fiber membrane manufacturing apparatus.

Claims

It is a porous hollow fiber membrane made of a thermoplastic resin, and has continuous irregularities in the membrane longitudinal direction of the outer peripheral portion, and the outer peripheral portion in the circumferential direction of the porous hollow fiber membrane consists of continuous irregularities. An irregularly shaped porous hollow fiber membrane characterized by
The sum of the length from the center of the porous hollow fiber membrane to the apex of the convex portion and the length from the center of the porous hollow fiber membrane to the bottom of the concave portion is the center of the adjacent porous hollow fiber membranes. The deformed porous hollow fiber membrane according to claim 1, which is smaller than the inter-space distance.
The said unevenness | corrugation is formed of the several recessed part and several convex part which were provided in the said outer peripheral part, The aperture ratio of the said recessed part is higher than the aperture ratio of the said convex part, The Claim 1 or 2 characterized by the above-mentioned. The irregularly shaped porous hollow fiber membrane as described.
The irregularly shaped porous hollow fiber membrane according to any one of claims 1 to 3, wherein a difference in height between the bottom and top portions of the irregularities is 1 to 320 µm.
2. The outer surface of the irregularly shaped porous hollow fiber membrane, wherein a value obtained by dividing the outer surface area ratio of the concave portion by the outer surface area ratio of the convex portion is 1.01 to 2.00 or less. 5. The irregularly shaped porous hollow fiber membrane according to any one of 1 to 4.
The unevenness is formed by a plurality of concave portions and a plurality of convex portions provided on the outer peripheral portion, and a ratio of surface hole diameters of the concave portions and the convex portions is 0.5 to 1.5. The irregularly shaped porous hollow fiber membrane according to any one of claims 1 to 5.
The unevenness is formed by at least a plurality of recesses provided in the outer periphery, and the ratio of the recesses in the entire outer periphery in the film cross section along the direction perpendicular to the film longitudinal direction is 5% or more and 100% or less. The deformed porous hollow fiber membrane according to any one of claims 1 to 6, wherein
The irregularly shaped porous hollow fiber membrane according to any one of claims 1 to 7, wherein a ratio of the irregularities occupying an outer peripheral length in a membrane cross section of the irregularly shaped porous hollow fiber membrane is 30% or more.
9. The irregularly shaped porous hollow fiber membrane according to claim 1, wherein the irregularly shaped porous hollow fiber membrane is a porous membrane having an isotropic three-dimensional network structure.
The irregularly shaped porous hollow fiber membrane according to any one of claims 1 to 9, wherein an aspect ratio of outer surface pores of the irregularly shaped porous hollow fiber membrane is 0.3 to 3.0.
The irregularly shaped porous hollow fiber membrane according to any one of claims 1 to 10, wherein a width of the unevenness is 1 μm to 500 μm.
The irregularly shaped porous hollow fiber membrane according to any one of claims 1 to 11, wherein the number of ridges in the outer peripheral portion, which is the number of the irregularities, is 1 or more and 300 or less.
The irregularly shaped porous hollow fiber membrane according to any one of claims 1 to 12, wherein the thermoplastic resin contains polyvinylidene fluoride and polyolefin.
By discharging the melt-kneaded product containing the thermoplastic resin and the organic liquid from the discharge port of the deformed nozzle for hollow fiber molding, and cooling and solidifying the melt-kneaded product discharged from the deformed nozzle, An irregularly shaped porous hollow fiber obtained by a thermally induced phase separation method is obtained by forming an irregularly shaped hollow hollow fiber membrane by molding and removing the organic liquid from the hollow fiber-like material after forming into a hollow fiber-like material having a modified cross section in a vertical cross section In the method for producing a membrane,
A method for producing a deformed porous hollow fiber membrane, wherein inorganic fine powder is kneaded in the melt-kneaded product.
The shape of the outer peripheral part of the said hollow fiber-like thing is formed in the said unusual shape nozzle by the some recessed part and convex part which were located in a line along the circumferential direction, The said shaped nozzle is formed. A method for producing a deformed porous hollow fiber membrane.
16. The method for producing a deformed porous hollow fiber membrane according to claim 14 or 15, wherein the hollow fiber-like product and the porous hollow fiber membrane have protrusions continuous in the longitudinal direction of the membrane.
The method for producing a deformed porous hollow fiber membrane according to any one of claims 14 to 16, wherein the pressure at the time of discharging the melt-kneaded product from the nozzle is 100 kPa or more and 900 kPa or less,
The melt-kneaded material runs idle in the idle running part until it is cooled and solidified after being discharged from the deformed nozzle,
The irregularly shaped porosity according to any one of claims 14 to 17, wherein air is applied to the melt-kneaded product at an angle from a direction that is not parallel to the idle running direction of the melt-kneaded product in the idle running portion. A method for producing a hollow fiber membrane.
The method for producing a deformed porous hollow fiber membrane according to any one of claims 14 to 18, wherein the thermoplastic resin is made of polyvinylidene fluoride, polyolefin, and a blend thereof.
The method for producing a deformed porous hollow fiber membrane according to any one of claims 14 to 19, wherein the plasticizer is hydrophobic.
Torque inflection of the melt-kneaded product measured by a plastmill, respectively, the resin temperature when the melt-kneaded product is supplied from the extruder to the deformed nozzle and the resin temperature when discharged from the discharge port The method for producing a deformed porous hollow fiber membrane according to any one of claims 14 to 20, wherein the temperature is higher than a temperature.
A hollow fiber membrane module comprising the irregular porous hollow fiber membrane according to any one of claims 1 to 13.
A membrane filtration apparatus comprising the hollow fiber membrane module according to claim 22.
A water treatment method for filtering a liquid to be treated containing at least one of an inorganic substance and an organic substance using the membrane filtration device according to claim 23.